Proton Mail is very much a work in progress, as a result, we will be frequently releasing new versions with bugfixes and additional features. Whenever a new version is released, it is usually good practice to clear your browser cache before continuing to use Proton Mail.
A good website we recommend for instructions on how to do this can be found here:
https://kb.iu.edu/d/ahic(new window)
Another website that provides information quickly (for the lazy), but doesn’t cover all cases is this one: