When using Connect Filter for Chromebooks to filter external users, proxy settings need to be used with IDex client too but that was not designed for external usage. The proxy settings can get in the way of WiFi login/accept pages when users try to connect to public WiFi locations.
If all outgoing web traffic from a client is sent via the configured proxy, accessing a local WiFi portal page can fail.
We will need to use proxy exceptions to address this problem. In general, exceptions for the proxy should be all private network ranges and a single IP as well, often used by Cisco access portals. Feel free to add to the list. Good items to have exceptions for are local domains, like your local Active Directory domain name. If you are hosting your PAC file externally, the host and domain name of the server should also be in the list.
Edit your proxy settings using your preferred method. Either by amending the proxy.pac/wpad.dat file that is used (often the case when Connect for Chromebooks is used), adding the proxy settings to the user profiles in Active Directory/Google Admin console, or by adding the entries to the "Web proxy - Mobile Proxy - Exceptions" field (this is for the SmoothConnect client). The list should contain at least:
Once those have been added to the exceptions list, reconnect the clients and test if their issues with public WiFi access have been resolved.
NOTE: This will not be an issue with the Cloud Filter solution as proxy settings are not required in that case.