command not working

Hey!
ive created simple mechanism that replaces naturally spawning mobs with armor into mini bosses, which i learnt in this server in the past. just today i was working on a new mini boss, trying to make it spawn naturally in the overworld using the same mechanism. but for some unknown reason it hasn't worked for this particular mini boss 
here are the commands:
REPEAT  UNCONDITIONAL  ALWAYS ACTIVE
execute as @e if items entity @s[type=zombie] armor.head minecraft:leather_helmet at @s run summon zoglin ~ ~ ~ {Health:800,equipment:{chest:{id:enchanted_golden_apple},legs:{id:golden_apple}},drop_chances:{chest:0.45f,legs:1f},attributes:[{id:attack_damage,base:20f},{id:scale,base:2.5f},{id:knockback_resistance,base:10f},{id:attack_knockback,base:25f},{id:follow_range,base:32f},{id:step_height,base:3f},{id:movement_speed,base:0.4f},{id:max_health,base:800f}]}
followed by a chain command block,
CHAIN  UNCONDITIONAL  ALWAYS ACTIVE
execute as @e[type=zombie] if items entity @s armor.head minecraft:chainmail_helmet run kill @s 
The zombie dies but the mini boss simply doesn't spawn.