Introduced by
632867: Editor: use one layout per editor instead of per document | https://codereview.qt-project.org/c/qt-creator/qt-creator/+/632867

It doesn't happen for all lines, but sometimes when I move the cursor to somewhere near the end of a line and press return to introduce a line break (breaking the line), the text from the end of the line that should move to the new line vanishes.

See video. text_vanishes.mov