you for reaching out on the community and telling us about your issue. I do apologize for the issue you're having. I'm wondering if we might be able to clean them up by going into the preferences menu. You can do this by going across the top to edit > preferences > data entry & quickfill. The last option should be delete memorized payees after a set amount of time. I would try making sure that's enabled and try to update transactions to see if that may help with some of those older transactions.
Once you get the chance let us know if this helps. If not we can take a look at what else we're able to find out.