When you archive or delete an email, or do anything really, a small yellow dialogue box appears at the bottom of the list of emails to offer you the option to Undo the action. This dialogue box floats atop the subject line of the bottom most email in the list. So if you are trying to manage about 1-page of emails in your inbox, that box stops you in your tracks until you either manually exit it, or wait out its timer to fade away.

It's a minor nuisance, but a very real one. The last email in the inbox is blocked every time you do just about anything in ProtonMail. So my suggestion is to move that box to right side of the list. Same vertical position, but instead of centered, 1/3 or 1/4th in from the right. This will leave the sender and most of the subject line unobscured, and reduce the likelihood of this action dialogue blocking the information you're looking for.

I'll probably go ahead and use Stylus to do this myself, as the CSS should be trivial. But it really ought to be the default behavior.