PDF’s missing from Books app

I had saved over 100 .pdf User Manuals for all the stuff I use. Been doing this for probably 10 years. Never had an issue before. Was in Books about 6 weeks ago and everything was there as usual.

Went in today and all .pdf files are gone from my Books app. No settings have been changed, Books is still toggled on in iCloud, etc. All actual downloaded purchased books are still in there. It is just the .pdf’s that are all missing. I had 100’s of them and they were important. Any ideas?