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Python requests.get only responds if I don't specify page number

I am scraping web data with python using requests and beautiful soup. I have found that 2 of the websites I am scraping from only respond if I do not specify the page number.
The following code works and allows me to extract the data needed:
headers = {'user-agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko)}
r = requests.get('https://www.milkround.com/jobs/graduate-software-engineer', headers = headers)
soup = BeautifulSoup(r.content, 'html5lib')
table = soup.find('div', attrs = {'class':'col-xs-12 job-results clearfix'})
If however I change the link to specify a page number, such as:
r = requests.get('https://www.milkround.com/jobs/graduate-software-engineer?page=2', headers = headers)
Then request never responds. There is no error code, the console just waits indefinitely. What is causing this and how do I resolve it?
EDIT: I opened the site in Incognito manually. It seems that when opening with the page number I get an "access denied" response, but if I refresh the page it lets me in?

That's because if you see, you are not able to access the page numbers on website from outside. So if you are logged in and have some sort of cookie then add it to your headers.
What I just checked on website is you are trying to access wrong URI.There are no page numbers. Did you add ?page= from your own?

The problem you're tackling with is about web scraping. In your very case, the web page you have blocks because your header declaration lacks of a proper user-agent definition.
To get it to work you need to include a user-agent declaration like this:
headers={'user-agent':'Mozilla/5.0 (Linux; U; Android 0.5; en-us) AppleWebKit/522+ (KHTML, like Gecko) Safari/419.3',}
You can dive more deeply into the problem of writing good web scrapers here:
https://towardsdatascience.com/5-strategies-to-write-unblock-able-web-scrapers-in-python-5e40c147bdaf
A list of proper user-agents can be found here:
https://webscraping.com/blog/User-agents/
Hope it get's you working with your problem.

How do I know which browser is used to crawl in Scrapy framework?

What's my context:
As you know, website HTML structure on Chrome, Firefox, Safari are quite different. So when I'm using CSS-Selector to get data in an element tag from HTML structure, sometimes It that tag is already have with Chrome browser but the other is not. So that, I just want to focus on only one browser to reduce my effort.
When I crawl data from urls by using Scrapy framework, I don't know which browser will be used by Scrapy to crawl data. Therefore, I also don't know what kind of HTML response body be returned. I checked the response and I found that sometimes the structure is the same as getting from Chrome but sometimes It's not. It seems that Scrapy framework used many different web browsers to crawl data.
What I want:
I want to use only Chrome browser for crawling data in Scrapy framework
The structure of the HTML response body must be obtained from Chrome
What I ask:
Does anyone have any Ideas or tips to help me deal with that issue?
Can I config the Webdriver in Scrapy Framework as Selenium does? (If It's possible, please show me Where and How?)
Thank you!

Scrapy does not use Browser, it parser for static html like BeautifulSoup. if you want to parse dynamic page (javascript generated) use selenium and if you want you can send the page source to Scrapy.
To set Scrapy to use custom user agent (Chrome), in settings.py add
USER_AGENT = Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.110 Safari/537.36
or in my_spider.py
class MySpider(scrapy.Spider):
def start_requests(self):
yield scrapy.Request(self.start_urls, callback=self.parse, headers={"User-Agent": "Your Custom User Agent"})

You can set the user agent in your setting file, something like this
USER_AGENT = 'User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36'
So for web server it will look like the request is generating from Chrome.

urllib getting HTML but missing data

Right basically I'm getting and displaying HTML which displays the data I'm looking for just fine in a normal browser but not in a HTML dump with urllib.
Example URL: https://betfred.mobi/sports/horses/event/4315034.2
Example data: Horse names like "She Is No Lady"
Displays just fine under a browser. Doesn't need any login or preexisting cookies or anything.
I thought maybe it was waiting to see an actual user agent or something but that should be fine as well. I'm setting one and I've checked - it's working.
opener = urllib2.build_opener()
opener.addheaders = [('User-agent', 'Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/43.0.2357.124 Safari/537.36')]
response = opener.open("https://betfred.mobi/sports/horses/event/4315034.2")
print response.read()
It's showing something alright and I'm getting a HTML dump of the site but horse names for example are not showing up.
Am I missing something blindingly obvious here?

If you need to handle pages with Javascript, try WATIR or Selenium - those drive a real web browser, and can thus handle any Javascript. WATIR Classic requires either IE or Firefox with a certain extension installed, and you will see the pages flash on the screen as it works.
At present, Mechanize doesn't handle JavaScript.
Your other option would be understanding what the Javascript on the offending page does and bypassing it manually, but that seems onerous.

Scrapy crawl blocked with 403/503

I'm running Scrapy 0.24.4, and have encountered quite a few sites that shut down the crawl very quickly, typically within 5 requests. The sites return 403 or 503 for every request, and Scrapy gives up. I'm running through a pool of 100 proxies, with the RotateUserAgentMiddleware enabled.
Does anybody know how a site could identify Scrapy that quickly, even with the proxies and user agents changing? Scrapy doesn't add anything to the request headers that gives it away, does it?

Some sites incorporate javascript code that needs to be run.
Scrapy doesn't execute javascript code so the web app really quickly knows it's a bot.
http://scraping.pro/javascript-protected-content-scrape/
Try using selenium for those sites that return 403. If crawling with selenium works, you can assume that problem is in javascript.
I think crunchbase.com uses such protection against scraping.

It appears that the primary problem was not having cookies enabled. Having enabled cookies, I'm having more success now. Thanks.

For me cookies were already enabled.
What fixed it was using another user agent, one that is common.
Replace in settings.py file of your project USER_AGENT with this:
USER_AGENT = 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/74.0.3729.169 Safari/537.36'

I simply set AutoThrottle_ENABLED to True and my script was able to run.

Get user browser info in Python Bottle

I'm trying to find out which browsers are my users using and I'm running into a problem.
If I try to read header "User-Agent" it usually gives me lots of text, and tells me nothing.
For example, if I visit the site with Chrome, in "User-Agent" header there is:
User-Agent: "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.57 Safari/537.36".
As you can see, this tells me nothing since there is mention of Mozzila, Safari, Chrome etc.. even though I visited with Chrome.
Framework I've been using is Bottle (Python).
Any help would be appreciated, thanks.

User-Agent: "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36
(KHTML, like Gecko) Chrome/31.0.1650.57 Safari/537.36".
As you can see, this tells me nothing since there is mention of
Mozzila, Safari, Chrome etc.. even though I visited with Chrome.
Your conclusion above is wrong. The UA tells you many things including the type and version of the web browser.
The post below explains why Mozilla and Safari exist in Chrome's UA.
History of the browser user-agent string
You can try to analyze it manually on user-agent-string-db.
There's a Python API for it.
from uasparser2 import UASparser
uas_parser = UASparser()
# Instead of fecthing data via network every time, you can cache the db in local
# uas_parser = UASparser('/path/to/your/cache/folder', mem_cache_size=1000)
# Updating data is simple: uas_parser.updateData()
result = ua_parser.parse('Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.57 Safari/537.36')
# result
{'os_company': u'',
'os_company_url': u'',
'os_family': u'Linux',
'os_icon': u'linux.png',
'os_name': u'Linux',
'os_url': u'http://en.wikipedia.org/wiki/Linux',
'typ': u'Browser',
'ua_company': u'Google Inc.',
'ua_company_url': u'http://www.google.com/',
'ua_family': u'Chrome',
'ua_icon': u'chrome.png',
'ua_info_url': u'http://user-agent-string.info/list-of-ua/browser-detail?browser=Chrome',
'ua_name': u'Chrome 31.0.1650.57',
'ua_url': u'http://www.google.com/chrome'}

Thank you everyone for your answers, I found something really simple that works.
Download httpagentparser module from:
https://pypi.python.org/pypi/httpagentparser
after that, just import it in your pythong program
import httpagentparser
Then you can write a function like this that returns browser, works like a charm:
def detectBrowser(request):
agent = request.environ.get('HTTP_USER_AGENT')
browser = httpagentparser.detect(agent)
if not browser:
browser = agent.split('/')[0]
else:
browser = browser['browser']['name']
return browser
That's it

As you can see, this tells me nothing since there is mention of
Mozzila, Safari, Chrome etc.. even though I visited with Chrome.
It's not that the User Agent string tells you "nothing;" it's that it's telling you too much.
If you want a report that breaks down your users browser, your best bet is to analyze your logs. Several programs are available to help. (One caveat, if you're using Bottle's "raw" web server, is that it won't log in Common Log Format out of the box. You have options.)
If you need to know in real time, you'll need to spend time learning user agent strings (useragentstring.com might help here) or use an API like this one.