Random Lines appearing on every page in Layout

[DaveR]

This is not specific to your scenes. It is an issue reported a while back and was supposed to have been fixed. Are you still using SU/LO 2019?

Edit: a little research turned up a post from Adam about this:

Strange display behavior in Layout 2020

Hi, This is a display only issue on macOS in LayOut 2020.0 that does not affect printing or exporting. It should only occur if you are zoomed in past a certain zoom level, which may vary per document. We are investigating this issue, but don’t have a timeframe for a fix. Sorry for the inconvenience, Adam

If you are using SU/LO 2020 update to the latest version.