How to reproduce
1. remove any armor you may be wearing (only happens when you start without armor on)
2. place any kind of armor into a dispenser
3. Stand in front of the dispenser in survival and activate it

Results
Armor will be placed on the player, but no armor icons will appear above your hearts. Opening your inventory updates the game and starts showing the armor icons. Screenshot below

Expected results
The armor icons should show

https://youtu.be/Hwq_V_FQhmo?t=538