Cursor jumping right, Writer loses place

I have a document (170,000 characters). I am editing and I place the cursor in the line where I want it, but when I type anything, the blinking cursor (not the mouse cursor) jumps off to the right past the end paragraph marker. When I try to edit, sometimes the characters are inserted in the wrong place, and sometimes not. FYI this is a desktop machine, Win 11, and I’m viewing at 160% zoom (trying to replicate a paperback book layout.
I started a fresh document, but this effect does not happen. I tried Direct Cursor and other than a different shaped blinky cursor, nothing changed. I made sure the actual mouse cursor is on the other screen, so it’s not an accidental click of the mouse on the document.
WAIT
I am using the Window → new window feature so I can keep my story calendar (an appendix in the document so I can keep track of story events) on the other screen. I just found that if I close the second window, the cursor acts normally again.
Cursor-wrong

I can open and edit WG60-WriterGuideLO.odt (751384 characters) in two windows at 160% without problems. It sounds as though it could be a graphics issue in your computer. You could try:

  1. Update the drivers for your graphics card(s). When I update the drivers for my laptop, it made a big difference, not just to LibreOffice. You might have to search the manufacturer’s or graphics card maker’s site for new drivers, not just rely on any tools provided in the computer.
  2. In LibreOffice you could go to Tools > Options > LibreOffice > View and tick the box Force Skia software rendering. If that makes no difference try unticking Use Skia for all rendering