Zombies with items (magma cream in this case, not tested with others) in offhand make the game crash.
Linked issues
duplicates 1
Comments 2
Thank you for your report!
We're actually already tracking this issue at MCPE-39589, so we will resolve and link this ticket as a duplicate.
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I replicated this on beta 1.10.0.4 using /replaceitem to put a nautilus shell into the offhand slot of a Zombie, a Husk, a Drowned, a Zombie Villager and a Zombie Villager V2.
In my case the Drowned was the only one to hold offhand items without crashing the game.