the fact that is sends (null) entries means it s failing.. just not fatally on your system.
If you still have the 1.6 .db's i d suggest trying to start anope from those and see if that fixes the access list.
also cleaning the entire list in sql will definately NOT, you are just making it worse. in fact the list is already empty, which is the problem in the first place... there are no entries in the list, yet anope expects there to be a number of entries. and when trying to access them it gets (null), when trying to add one after the last one it thinks is there (but is not) it fails.