Each plushie or beanbag I try to play with, I get this message: Err... that was SO boring! Is this happening to anyone else?

Your pet is already at full happiness. If they're in the resort or have a minion attached, you won't need or be able to play with toys.

It's not a glitch, when your pet's happiness is at 10 they refuse to play with anything. In order for your pet to have a low happiness level, take off their minion for the time being. Or just wait for their happiness to go down a few points. (if they don't have a minion)

Ah! Thanks! I had been trying to do some Major Drill quests yesterday, and ran into this.