Great post.  Completely wrong, but great post.  This has been an ongoing issue for years and happens on old files, new files, rebuilt files and in every version of QBD for as long as I remember up to, and including 2021.  

Adding or editing rules starts fine but the time to enter the edit page increases with each new edit and after about 10 edits, can take an interminable amount of time to open the edit page.  Exit QBD, reopen the file, and again, it starts fine and begins to stall after another 8 to 10 entries.

If you're telling me to rebuild the file as a solution, I doubt you spent the required time to test your "fix" before posting that.