Troubleshooting Tip: Windows 10 browser popup with 'Click to connect' prompt.

This article discusses the behavior where Windows 10 browser automatically displays the following message when isolated:

'Connect to a network
The network being used may require user to go to its sign-in page. Select connect'.

This behavior can occur if there are domains that are required to resolve when isolated.

1) Identify which domains the host is querying that are not resolving.

2) Determine which of those domains should be added to the Allowed Domains List.

3) Once those domains are added, re-test.

For details see related KB article

https://community.fortinet.com/t5/FortiNAC/Technical-Tip-Troubleshooting-domain-resolution-in-the-captive/ta-p/191914.