Markups on pdf in iCloud disappear

I use my iPad (2019 12.9” pro) to annotate PDFs. The documents are all in iCloud and I open/annotate them in Files. Multiple times I have been pages into annotating a document and all my notes suddenly disappear and I am unable to reverse the action or get them back. This is infuriating as it has deleted hours worth of work. How to I stop this from happening or get my edits back when it has happened?