Not A Bug Air Ballon not announced

[Mwoonn]

What type of bug are you reporting? Mechanics

What is the bug?
Magic room: if a pokemon is swapped in during magic room its Air baloon is active but not revealed after magic room ends

Are you able to replicate it? If so, how?
Set magic room > swap to air baloon pokemon > after magic room ends its air baloon is active but not displayed
example replay: turn 12 https://replay.pokemonshowdown.com/gen7ou-2378331484-2w5hcvyd8i5brj852h07f2d4a2661gspw

 

[Irpachuza]

I believe this is not a bug, might need someone with cart experience to confirm.
Air Balloon displays on PS because when a pokemon holding it enters the battle there is a system message announcing its item. According to Bulbapedia, for Air Balloon this message only appears if the item's effect is not being negated. So if this is correct, then when Magic Room expires there is no reason for announcing Air Balloon if the Pokemon was already on the field, which is the case in your replay.

Edit: Seems to be the same that happened here, confirmed on SV cart