I’m also having issues as of late, I started a separate thread before coming across this one:
Now when I try to open the mail app it jumps around to various pages. I occasionally get an error “this app has stopped” with an option to close the app.
Other times when I open the app it just disappears without me trying to close it. Super strange, I’ve been using my Fairphone 4 for months now with few issues with the Mail app until recently.