Concentration checks seem to be in game, just not in the combat log (where they should show). But I've seen a dice rolling above a character's/enemy's head when taking damage, and only on a failed result it says concentration is broken. I'm putting this on early access right now, but the UI definitely should be improved. If I didn't know D&D 5th edition already pretty well, I'd be quite confused on how the hell these mechanics work.
