For the last 1.5-2 months I have had similar stuff .. *Specifically* with the BYC APP ONLY:
click on either "envelope OR Alerts" and for a nanosecond the page list will let me choose one of the "alerts" and as soon as the onscreen keyboard shows up it vanishes. and I try to "mouse click" on the space where you write text and the keyboard will show up for just over a nanosecond then disappear again.
meanwhile I will feel the phone start to heat up as well., It has heated up quickly when I have struggled with trying to get the on screen keyboard to show up for a reply in thread.
The App also has an oddity for the "alerts" for either threads or conversations; once I select on of the updated and i'm done and want to go back to fin d the next alert. they have ALL bee flipped to "having been viewed" status.
iphone 11
all currently updated.
battery heats up and any level