As another user noted in my other topic, and this is also an issue I've been experiencing (but I didn't report it before because I thought it was just the new lag caused by Satpatch), the heavy attacks are semi-broken after Sat's patch as they often don't work.

Basically, often the heavy attack doesn't happen, instead your character puts their arm with their staff forward and retracts it again and nothing happens, and sometimes the staff lights up orange/yellow for the attack as well and then powers down, and the character retracts the staff and nothing happens.

And sometimes nothing happens at all when you keep holding the heavy attack, so you have to do some light attacks first before suddenly the heavy attack starts working.

https://forums.elderscrollsonline.com/en/discussion/comment/3531337#Comment_3531337