Check your weapon damage, if it goes down also then you have an issue with the spell. If it goes up, then it’s just some weird client issue I’ve noticed it on servers with high stats especially when modifying attack power directly and not indirectly through other stats like str and agi, it seems when it calculates your attack power that whatever variable that stores the attack power overflows. So like let’s say some reason it’s a short int once you go over 32,767 attack power it rolls over to -32,768.
This didn’t seem to actually effect anything just seemed like a visual client issue only. I didn’t end up looking far into it though, so I could be wrong. Also might not just be a short int could be another variable it’s just what I’m assuming it would be.