Quote from SuperGamerRob
Aether accesories (rings, capes) do not stay in your inventory with keepInventory gamerule enabled.
Same goes for gloves (incase you dont count them as accesories) though aether armor (zanite, gravetite, valkrie, etc. chest, helm, boots, legs) do not dissapear. (same for sentry boots)
This is a known bug that is being worked on.