Logged in after today’s patch and noticed my armor was pretty banged up. I’m wearing a set of epic exceptional Aquilonian Infantry armor. Master armor patch kits repaired every other piece as normal but would not repair the sandals despite being consumed on the attempt.
Repairing them via thrall in the armorer’s bench using hardened leather did work fwiw.
I haven’t tried any other armor sets so can’t say if this is set or slot specific.
Edit: After further testing it appears the issue is not tied to slot or armor but to the amount of patch kits in the stack that is being used. If there’s more than one kit it will work as normal. If there’s only one kit however it will be consumed but the armor piece will not be repaired.