I have a Pro 9.7 and didn’t encounter a similar problem at all until today when copying text from Notability to Notes. Suddenly, Notes just crashed every time I tried to open it. I tested to see if the problem was duplicated on my iPhone. The app opened properly, but I found a new note titled “New Note Handwritten Note” that I did not intentionally create at any time. I don’t know if it was related to the process of copying and pasting from Notability or just an accidental note created while using my Pencil. I was not aware of any handwritten notes or markings in the text I was copying but had been using my pencil with the MyScript Stylus keyboard to enter text as needed in Notability. I tried to open the note on my iPhone to check the content and the application crashed. I was able to open the app again and delete it from the list and Notes has worked fine on the iPhone from that point.
Next, I tested to see if Notes on my iPad was working and if the rogue Note was in the Recently Deleted foldee on the iPad but still was not successful in opening the app. I decided to turn off iCloud sync on the iPad, which deleted all notes. With the rogue note successfully deleted on the iPhone, turning iCloud sync back on for the iPad resulted in all my notes loading properly. The app is now working properly.
The note was still on my iPhone in the Recently Deleted folder, so I tested to make sure it was the problem by trying to open it and the app crashed just as before. I have permanently deleted it and the app is now working properly on both devices.