Try to log-in on this website with a previously registered account
Actual Result:
If the Brave shield is active, then log-in fails on the website (see error message on the screenshot below). By disabling the Brave shield, I can log-in without any problems and with the same browser settings (except Brave shield).
You can play around with shield settings, on a site by site basis. Try moving strict settings to standard, or allowed, cookies from cross site to allowed. Change one and not the other etc to find out which is possibly clashing with the website whilst maintaining the highest privacy settings you can.