Files app crashes but reloads to a previous saved moment

I’m trying to write math on the pdf handed out by my professor on my iPad in files, when all of a sudden the files crashes inside the app but not fully where it will reload to a point it has previously saved the file. Losing a significant amount of work to catch up and write. I tried finding out how to avoid this issue but when I think I found out how to avoid it. The problem comes back, not knowing what’s causing it.

I tried renaming the file, restarting my iPad, avoiding the smoothing feature, editing it in the cloud, and using only one pen option. Anything that I think is causing the problem is not it.

The only way I now that will guaranty my work will be saved if I exited out and back into the file. Which is starting to get annoying.