Pen Marks Disappearing

I take notes on my ipad. Sometimes when I open a note, it looks like someone used the eraser tool on object mode and drew a line directly down my notes from top to bottom. The note is so long there’s no way I could’ve done this by myself on accident. It’s happened twice and I had to rewrite the letters myself. The note is long and idk what I could’ve done to make all these pen marks disappear. I might just switch to good notes by this point if I don’t figure out why this is happening 🥲