Getting error "PDFDocument: Stream must have data" after opening .pdf from stored variable between sessions

I save .pdf file to a stored variable and open it in the same session (in a different screen) with pdf viewer , it works properly and opens the file as intended.
However, when I start another session, I get the error thats in the title. It looks like the .pdf file isnt in the stored variable anymore. Does anybody know, what can be the problem here? I have no knowlege of the file being removed between sessions, the variable also isnt empty - when I tried putting the file into a label (for test if its empty) I got some weird thunkable link starting with blob - probably the local database for web viewer.
Other stored variables (integers only) are working properly, only this is a problem.
The problem is also present at .apk version of the app.

Thanks for help.