Tickets not closing due to undetected subcategory

Just upgraded from 9320 to 9323 so I'm not sure where the problem is, but I've got one. Typically, to close a ticket I go to the Resolution panel, enter my info, then set it to Closed when I Save. Now, it will save my Resolution text, but the ticket stays open with a message that says it cannot be closed without a Subcategory. Subcategory is a required field, so the ticket wouldn't be created without it.

When I go back to the Request tab, the Status is still Open, even though there is a Subcategory entered. If I click on the Subcategory, it opens the pair of Category/Subcategory dropdown lists. Without changing anything, I click the green checkmark and it will save the Subcat and set the Status to Closed automatically.

Is there a new setting somewhere or is it somehow not recognizing the Subcat? This is happening with tickets created both before and after the update.

Example pictures attached. 1 shows the state of category and subcategory when I open a new ticket, and 2 shows the message I get when I try to close it.

Any ideas are appreciated.