There is this certain buff you get from hallowed armor wich makes you invincible for the next attack. however each time you get the buff it counts as unfair and you get frozen and all buffs including potions buyed from chest get deleted its really annoying and not fun at all. this happend on death house as mage class. might also apply to other maps.
Reason being, likely, is that the server counts that as a banned or hacked buff so it gets rid of every buff to prevent you from using it. I may be wrong but it surely is a reason!
I think this banned buff has been addressed - as all other banned buffs in Zombies - a while ago. If not, I guess it’s another one for the developers to deal with then.
When did you experience this buff? It was resolved a long time ago and in my client it works correctly.