Can't connect second controller on nintendo switch for co-op

I’m trying to play couch co-op on diablo 3 eternal collection on my switch. The switch, the controllers, and the games are all up to date. I connect two controllers to the console but as soon as it launches, it disconnects the second one and there’s no way to reconnect it and no co-op options on the screen anywhere.

You figure this out? It’s outrageous that it’s so difficult.

No, I never did. Seems like its not possible anymore.