the helmet will slowly break due to the sun and will kill the zombie, to fix this put him in water, put a mob/player head on him or just put a block above him, also you can change the zombie to a pacified pillager or husk to not burn
okay i solved this. it is to do with optifine so if anyone has this then stop playing on optifine
except it doesn't, you cannot craft levers out of blackstone
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21w11a still has it
Woops typo yeah i meant seagrass