I have installed Ubuntu 17.10 on my laptop, and there have been a host of problems with wifi. The one that I am trying to solve right now is the fact that it connects to a network, but it does not load the captive portal. When I open a browser to load the captive portal, it also fails. I have tried resetting network and NetworkManager, both of which fail after timing out.
My laptop is an Acer Aspire E 15 E5-575-33BM.
Best Answer
Captive portals are weird.
You may just need to visit a non-HTTPS web page to actually trigger the captive page loading, as HTTPS pages can't normally be intercepted/redirected by the gateway.
One such well-known example of a non-HTTPS site is http://captive.apple.com, and is actually what Apple products use to check for a captive portal. Another well-known page is http://www.msftncsi.com/ which does (roughly) the same thing for Windows devices. There are many others on the web as well if you'd rather use those.
Try using one of these in your browser first, and it may cause the captive page to kick in and load.