Armour on mobs are appearing and disappearing on mobs at random times, (seems to be right before it gets hit by a trident). Not sure if it is a visual thing where it doesn't render, or something is actually happening to the armour. Seen it happen for gold and leather armour, for all the different armour pieces. Probably happens with other materials too.

Unsure how to replicate, happens randomly, but quite frequently. These mobs are from a spawner.