During the last hour, I got three pop-ups on my workstation (which is connected over Ethernet) with blank windows and a title that read "Captive portal". Two of them turned to the gnome.org home page, while the other one just disappeared.

In my journal I have this sort of errors:
Mar 26 03:39:36 <hostname> NetworkManager[1006]: <info>  Connectivity check for uri 'https://fedoraproject.org/static/hotspot.txt' returned status '403 Forbidden'; assuming captive portal.
Mar 26 03:39:36 <hostname> NetworkManager[1006]: <info>  NetworkManager state is now CONNECTED_SITE
Mar 26 03:39:36 <hostname> NetworkManager[1006]: <info>  Connectivity check for uri 'https://fedoraproject.org/static/hotspot.txt' failed with 'Error performing TLS handshake: An unexpected TLS packet was received.'.
Mar 26 03:39:40 <hostname> NetworkManager[1006]: <info>  NetworkManager state is now CONNECTED_GLOBAL
Mar 26 03:39:46 <hostname> NetworkManager[1006]: <info>  Connectivity check for uri 'https://fedoraproject.org/static/hotspot.txt' failed with 'Error performing TLS handshake: An unexpected TLS packet was received.'.
Mar 26 03:39:46 <hostname> NetworkManager[1006]: <info>  NetworkManager state is now CONNECTED_SITE
Mar 26 03:39:48 <hostname> NetworkManager[1006]: <info>  Connectivity check for uri 'https://fedoraproject.org/static/hotspot.txt' returned status '403 Forbidden'; assuming captive portal.
Mar 26 03:39:49 <hostname> NetworkManager[1006]: <info>  NetworkManager state is now CONNECTED_GLOBAL
Mar 26 03:39:55 <hostname> NetworkManager[1006]: <info>  Connectivity check for uri 'https://fedoraproject.org/static/hotspot.txt' returned status '403 Forbidden'; assuming captive portal.
Mar 26 03:39:55 <hostname> NetworkManager[1006]: <info>  NetworkManager state is now CONNECTED_SITE
Mar 26 03:39:56 <hostname> NetworkManager[1006]: <info>  NetworkManager state is now CONNECTED_GLOBAL

Is this supposed to happen or do I need to file a bug report?