The recent ProtonMail for Android 4.0.4 update logged me out and I missed some important emails. I only realized the update had logged me out when I wondered "why haven't I received any email for the past few days?" and opened the app.

Please don't log users out when you update your apps. Or if that's unavoidable, at least send a notification to say something like "ProtonMail was just updated and we had to log you out. Please log back in so you don't miss any notifications"