I think it has been a problem for many versions. For me, it seems to do with copying (lyrics or melody) and then possibly removing them. This can happen if you copy (alt-c) either from the wrong bar or to the wrong bar, then use undo or cntl-z to clean up the error.
Lyrics and or melody from another part of the song will often show up in the first bars of the song.

I only use unfolded format, so it probably isn't that. My guess is UNDO is the culprit. It's very frustrating and can be a nightmare to clean up.

BIAB for Windows Version 2019 (643)
Windows 10 (1909)