Hi,
The one issue I know is that if you are using Nginx and are using multiple domains for your Matomo instance (like matomo.onesite.example and matomo.anothersite.example) then the login might fail on the secondary domains.
This is because by default nginx sets the SERVER_NAME variable it passes to PHP to the host of the first entry in the server_name list. But Matomo uses this variable for a host check and if it doesn’t match (which happens on the secondary domain), the login fails.
One solution for this is to add
fastcgi_param SERVER_NAME $host;
directly before the
fastcgi_pass unix:/var/run/php/php7.3-fpm.sock;
line. (so after any snippets/fastcgi-php.conf line)