Hello,
Thank you for supplying your user key - from the key I am only seeing one repeated error:
"Document properties failed to be retrieved.......no item with the given ID could be found"
For full transparency, I am not an engineer but my interpretation of this message is that the add-on is unable to locate these files and that can happen for a few reasons:
1. The permission settings on the file are not open
2. The folder holding the file is not accessible to the add-on ( if it was on a Team or Shared Drive or if the sharing permissions on the folder are not open/ belong to another account)
3. The Doc Appender settings were created when more than one Google account was open ( my previous reply on resetting the triggers would have covered this scenario)
4. The folder was created by Google Classroom - there is odd behavior occurring for some users with folders created by Google Classroom, it is an open issue that I am unable to recreate but a few users have reported that Doc Appender does not work on a folder created by Google Classroom.
I'm not sure if you have already tried this but as a test, I would suggest creating a new folder with new documents and have that folder live at the top of your Drive ( not stored in another folder) and see if that resolves the issue. Hope something here helps!