I am not 100% certain I get the errors on WPEngine (still debugging that for sure) but I def get them on 7.3 on MacOS – have you tried 7.3?
I am using 7.2 which is what WPEngine uses.
Evidently the settings don’t really work for subcats. You have to set that in each category manually under category editing. Haven’t found a way to set a default.