Temple Medallion +1 fails to increase slot

I've seen it happen a couple different times now.

I have an open slot, pick up the medallion and see it as an option to use.

Upon consuming the medallion, it doesn't increase my max slots.

This has happened on two different characters now.

One character is 0/5 slots max, the other one is stuck on 0/3 slots.

Essentially, not able to increase the max capacity when using the medallion that increases capacity.