When effected with the invisibility effect, Armor stands will not show equipped Armor, with the exception of carved pumpkins or mob heads.
chestplates helmets etc become invisible with the Armor stand for some reason.
MCPE-42372
Armor stands do not display Armor when invisible
Resolved
Fixed
1
Miles Davies
(Unassigned)
387295
Confirmed
Multiple
1.9.0, 1.12.0
1.16.201 Hotfix
Retrieved
It happens to me too. This needs to be fixed!
Edit: I also duplicated this report "MCPE-43941." After this bug is fixed I'll be able to make my collectables within minecraft, which is very easy to make and will spice up an adventure map...