In my current playthrough I had Shadowheart casting Owl's Wisdom on my character to help with passive Perception checks (I hate missing things) and my party was hit with Grease. Shadowheart failed the Dexterity check and instantly lost Concentration? As far as I'm aware that is absolutely not supposed to happen as per 5e rules, which state falling Prone doesn't cause loss of Concentration - but that a DM might feel the circumstances merit a Concentration check. Even if you interpret this as applicable, surely that means a fresh Constitution check should be applied to see if Concentration is lost, not have it be instant and guaranteed? Otherwise that seems like a ridiculously powerful mechanic to be abused by players and the AI...

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Concentration is perfectly sensible mechanic that tracks in universe as well as systematically - granted some spells should not be concentration when they are, and other should be when they aren't; the system isn't perfect, but in general the concentration mechanic exists for a valid reason and does its job. In Larian's game, however, they've bombarded players with situations that force many, many more concentration checks than should normally come into play, and also created unavoidable condition infliction that automatically breaks your concentration - as opposed to a normal game of D&D where you might make one, maybe two concentration checks between one turn and the next, IF you're actively being harried. In BG3 you'll often have to make several successive concentration checks in a row, or just get handed an auto-fail that had no chance of not breaking your concentration automatically... The game is tailored strongly to make people hate the concentration mechanic and think that it's bad, because it's extremely difficult and often impossible to maintain your concentration for any useful amount of turns at all.

Going prone breaking concentration is still in BG3 because falling prone inflicts you with 'unconscious' which is ridiculous. Unless they fix the mess with status conditions, this isn't likely to change - and it means that right now in bg3, a goblin over the other side of the camp, can shoot at you with disadvantage from long range, roll a natural 1, miss you entirely, and STILL break your concentration because they used one of their magic arrows that still knocks you down even on a miss. How they thought that giving common enemies a *literally guaranteed* way of breaking your concentration whenever they want was a good idea is beyond most people here.

Edit : Ok I swear I wrote this before seeing @The_Red_Queen edits 😅