It’s probably due to stat exp. You gain stat points by fighting different mons up to a certain point.

https://gamefaqs.gamespot.com/boards/198314-pokemon-yellow-version-special-pikachu-edition/44331699#:~:text=Stat Exp is a number,individual amount of Stat Exp.

I didn’t look anything up yet. But can the wireguard tunnel be setup on the router level (I have a cheap Mikrotik) or as a network service? So clients don’t have to install custom stuff