PDF documents saved in the research folder become unreadable after some time

What I normally do:

  1. create a project and document to write in
  2. save a PDF file in Scrivener work environment so I can refer to it or come back to it later
  3. use split screen so I can write while looking at the PDF document
  4. after some time passes (~ one hour?), the PDF becomes unreadable, only images and tables are visible (see attachment)
  5. have to reupload the document so I can read it in Scrivener again

I thought it’s a one-time bug but it’s happening consistently. There’s no official bug/error message, it simply doesn’t work the way it should. I’m just making lecture notes now but I wanted to use Scrivener for academic writing as well and if the bug persists the software would be unusable for that.