Ipad not saving notes on pdf

Every time I write down notes with my Applepen on pdf my Ipad does not save them even when I re-save the file so that it gets updated with my notes. I have already tried seeing if it's an issue with the iCloud uploading the backup of my notes, but it happens the same when I save the pdf with my notes on the device. It's been pretty inconvenient and a source of frustration; all my lecture notes of the recent weeks have just been thrown away out of a sudden.

It is a shame I'm having this experience with the first Apple device I own; I purchased my iPad with high expectations of product quality and UX (that's what everybody says) but so far my iPad has only been a source of frustration because it cannot efficiently and easily perform a simple task like automatically saving notes on PDFs