PDFs disappeared after markup with Apple Pencil

Many PDF files saved locally ("On My iPad") have disappeared after markup in Files App. I had spent over 6 hours to add notes to the pdf and its inaccessible now, that too a week before an exam I have been preparing for over an year!!

its utterly frustrating and Apple has been of no help. I spoke with the customer rep through Apple Support and they tried to help, but didn't have any solution expect to say "its a known issue". Had I known bout this known issue, I wouldn't have relied on the markup in the first place!

The Issue:

I downloaded some PDFs for revision for my exam. While reading them I made notes on the PDF itself using markup with Apple Pencil 1st gen. When I opened the Files app the next day, the aforementioned files were not present in the respective folder. Of the 7 PDFs in this particular folder, only 3 with markup done on them have disappeared while the rest are still there. When I am looking up the file names using search option in Files, I am able to see those files but no action can be done of them - I tried copy, move, open folder location, markup, share - but nothing is working. When I select the "Get Info" option after long press, the location is coming up as "Calculating..."

Is there any way for me to access these files or recover them in any way?

[This is an Urgent request, need someone to help me out before my exam :'/ ]

i am using iPad Pro 10.5" with iOS 17.5.1