What happened: The text moved upwards beyond the screen view and the line being typed gets placed at the top. For every subsequent next line the behaviour repeats.
What did you expect to happen: The active line and text should remain where it was while typing.
The bug starts happening if you open the link editor that’s next to every external link. You need to kill the app from app switcher to get back to normal, and then never open the link editor again until it’s fixed.