I have 3 Porcupine Pet and after doing the quest where you are able to use 3 pets at once, I tried equipping the Porcupine Sunglasses to each of them. Now the problem is that 2/3 of the Porcupines have the equip while the last one would not be equipped.
After testing https://royals.ms/forum/threads/pets-disappear-when-changing-channels.194206/ pressing cancel after selecting the pets, The equipment works normally.
It's a known bug, the Devs are unable to fix this yet Pressing Cancel will avoid this multi-pet glitch