The PlayerUtils.isPlayerReal function checks for an explicit instance of ServerPlayerEntity.class, however Galacticraft is hacky and replaces the player with their own custom player class.

This is creating an issue with Armoreablemobs Gamestage support as it uses this function to check if nearby players are real before checking their game stage. With Galacticraft, this means the check always fails. I'm assuming there are other mods that might be affected by this.

Turns out I should do more research as adding PlayerAPI resolved the issue.

As an API used by other mods maybe you should look into baking in GC support, but that's up to you.