Cauldron 5-set charm bonus is supposed to give stacks and does most of the time, and then give a buff, and then restart building stacks. However, sometimes I completely lose the ability to gain stacks! What helps is:
- putting the item in and out of its socket (hairy in combat)
- dying (sometimes acceptable enough)
I’ve seen it in most content, but can be most reliably reproduced in Infernal Hordes.
At the start of each wave I stop being able to get stacks. I think it has to do with some state where I leave combat and stacks are supposed to reset? But I never regain the ability to get them. I don’t know really what causes it.