Torrc modification doesn't work, even though Tor test page indicates that it does.

Operating System: TAILS 5.7
Tor Browser version: 11.5.8
Tor Browser Security Level: Standard

I modify torrc (/etc/tor/torrc) with the ExitNodes command. The Tor test page shows that this change was successful.

However, website info shows that my IP address is different from that shown on the Tor test page. This IP changes periodically, or if I reload the site. This happens on multiple sites.

What is happening?