locked Pokemon in PC after trade

[Darkillalala]

Hello.

I need help with a Pokémon that became trade-locked in my PC.

A player with the nickname Dergoraner asked me to help evolve their Pokémon via trade. They traded me Clamperl holding Deep Sea Pearl for evolution.

After the trade, the Pokémon appeared in my PC storage but it is completely locked. I cannot move it, trade it back, or interact with it in any way.

Right now it is just stuck in my storage box and I cannot return it to the owner.

Could you please tell me what I should do in this situation?
Do I need to unlock a specific region, complete a quest, or is this a bug that requires staff assistance?

Thank you.