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
21w11a still has it
Woops typo yeah i meant seagrass