I have a Poké Gift that is claimable by each player once. It contains an Eevee.
This has existed since 8.2.0 so I'm not sure if it has already been changed.
If someone obtains multiple of these gifted Eevees, such as from a trade, only one of them can be used at a time.
Sending out one of them marks the others in the team with the green background as if they are out, but they are not.https://i.imgur.com/ESJnYDh.png
When used in battle, you cannot switch between them.
They must have the same internal ID number or something.
This seems like a big oversight for the Poké Gift.