I always roll 175+% pack size for harvesting gold…
This occasionally happens:
-Notice the absence of the HP bars above their heads.
-These “Zombies” are non-hostile objects which will follow the MC as long as he/she is within aggro range.
-They neither attack nor deal damage, but they have collision (especially annoying for non-AoE builds)
-Apparently they still drop their loot and gold despite being “Zombified”. Toasted with zombified Enslaver, there was a pet lingering around where the Enslaver was.
My device is not a flagship but it isn’t a throwaway device either. High or low graphics make no difference, so I suspect it is some sort of graphic bottleneck (I am no expert though 
).
How to reproduce the “Zombies” bug:
-Gather hordes of monsters until the device lags to a crawl
-Kill the mobs you have collected
-Some of the horde will be “Zombies”
What I suggest as solutions or workaround:
-Do not render mobs beyond a specific population
-Spawn queue beyond a specific population
-…or maybe something else. I’m just making intuitive guesses lol