Armour stand gone when put netherite armour after went to Netherworld

The armour stand equip with netherite armour vanished/gone when I come back from netherworld for a period of time. The incident happen for a few time, I have try equip the armour stand with craved pumpkin but it's does not vanished. But when I put craved pumpkin and netherite armour, the armour stand gone. Thank you.