I got this event

Bandit challenges you to a fight in the Battle Coliseum!

but he's not in the coliseum when I go there.

Have you checked the "Events" tab?

He stole three of my items then stopped stealing my items. I didn't get an event and I checked in the battle coliseum under the events tab, and he is not there.

Did you actually get the event where he challenged you? You have to get the event to unlock him, just having him steal an item won't unlock it. It can take a few thefts before you get the event.

He stopped stealing my items though, I thought when he stopped that means he's unlocked... I'll keep throwing items in though.

Hmm, then maybe something is glitched. Hopefully it gets sorted out soon.

I got the random event, and he isn't in the coliseum for me either

I didn't realize there was an event tab. He is in there. Thank you so much!

Same thing with me ' he challenged me and dosn´t show up in the Coliseum.

Me too. Got the hidden opponent event and no luck spotting him in the coliseum