I think this problem is "Captive portal detection". It mentions
here that this capability first appeared in Windows Vista, and I have essentially no experience with Windows versions newer than XP, but no doubt someone with sufficient Windows technical knowledge could do better than
it could be anything.
Some technical references here:
https://technet.microsoft.com/en-us/...17(WS.10).aspx
...but I don't see any straightforward troubleshooting checklist.