depending on the macro usually its locking up because a spell cant fire in a sequence for some reason … look in the macro for the /castsequence … look for a spender spell and thats the one usually locking it up
One thing that will always lock it up for me is if you have /uss Heart Essence in the macro, and you are not level 120 and don’t have an essence to use.
It doesn’t only lock it up, but it also kills the interface.
Another thing that can sort of lock it up is if you have a trinket with targeted effect and your macro activates it.