I have chased a few false trails and was stuck with a checkout error on all items. When checking out books, we kept receiving "No circulation rule is defined for this user and itemtype combination." On checking, all circulation rules were defined as necessary. Rules were in place for both Books and DVDs, for all user categories. We managed to get it to work by placing another rule for 'All' categories, 'All' itemtypes as an overhead. This should never be used following the hierarchy of the rules, but it seems to allow all of the other rules to now be followed (they have become valid). This has a workaround - the all/all rule, but it would be good to know what is going on. It is also good to note that this was working before on 18.05!
It's generally recommended to configure an All-All-All rule as there are some cases where it's needed. I think one of the cases is when the record has no itemtype set, but it's needed for max holds calculation. Could this be the case here?
The version this was reported against is now very old and reporter didn't give any more feedback. Closing.