Hello there @mk7z please accept my apologies for this inconvenience. Please go to your shields widget by clicking on the Brave logo > Upgrade connections to HTTPS > toggle it off.
Since the issue with Protonmail doesn’t (didn’t) occur at all with proton.me but did consistently with protonmail.com, the reason for that is still unclear (isn’t it?).
Protonmail, which has been investigating the issue on its end, has advised that “it seems that one exit may be banned”. I don’t know what that means, but maybe you do (?)