Missing markups for pdf in notes app
I am a student and I use the notes app on my iPad sometimes to take down important information in class. However I realise that when I use the notes app to markup a pdf file with my Apple Pencil, all the markups/ half of them would disappear when I exit the pdf file. This has happened multiple times which is extremely frustrating. My notes are not saved on iCloud. Is there anyway I can possibly fix this issue or at least recover my missing markups?
iPad Pro 10.5-inch, Wi-Fi