I’ve mainly only noticed this on Chromaggus during arcane vulnerability, but EVERY mage I spoke to says they experience the same thing. It’s like there’s pushback happening without taking damage, sometimes only 2 of the 5 missiles will fire before the cast ends. It’s completely busted and has been for months.
The combat log seems to indicate WAY too many ‘casts’ during the act of channeling the spell. There is only one cast per 5 missiles, similar to mind flay, not 5 casts:
Yeah apparently AM is taking a debuff slot so what’s happening is during a arcane vul all the mages start casting AM but if there aren’t enough debuff slots for all of them to cast AM then they start knocking off AM from other mages. Then the mages who got their AM canceled start casting again and knocking off someone else AM and the cycle continues. You can test it by just having one mage cast AM during vul phase and their AM should last the entire duration. Apparently, the same sort of thing also happens with casting blizzard on firemaw, if you have too many mages doing it then they will start knocking off blizzards and cause some people’s blizzard to end prematurely.