Unreadable text when most recent project is displayed

When Scrivener loads up on my laptop, it displays the last project I was working on. Unfortunately the text is hidden, or rather the paragraphs have turned into lines of black blocks. I have just bought Scrivener and don’t know if this is something other people have encountered. I’ve googled searched the issue and have found nothing about it.

My older novel chapters occasionally do this as well. It changes to black bars matching the text exactly.
To correct the problem, I highlight the entire chapter of black lines, right click, choose [Highlight Color] and then choose [Remove Color] (it has a box with a slash)
My text returns to normal, readable text, the way I last left it.

WHY it does this, and what I am unknowingly doing to make it change, I don’t have a clue, I’m certainly not saving it that way in the first place.
Hope this helps.

Are you by any chance syncing your project using DropBox and/or sharing with iOS Scrivener and/or with another PC?