Steps to reproduce
Click end of a line. Press enter. Nothing happens.
Backspace all the text of the line. Text erases. Backspace again. Nothing happens.
Drag-left the line and click delete. Works.
Kill the app. Start the app. Backspace works. Enter works.
Environment
iPhone 8 app. iOS 13.
Additional information
It happens sporadically, but on multiple occasions.
The lock button is off.
Things to consider: I may have entered data outside the app and sync triggered the issue. It may have something to do with an extended idle period, say overnight.