Concentration in BG3 can be frustrating, due to the increased amount of guaranteed Conc. saves you are forced to make compared to 5e, along with other factors that others have already mentioned.
The Concentration save that you make when you take damage is a Constitution Save DC = 10, or half of the damage received from that instance of damage. So whether you take 1 or 20 damage at once, you will make a DC 10 CON save. Once you take more than 20, the DC will begin to increase. When you take multiple sources of damage at once, you make a conc. save for each source of damage.
This is balanced in 5e, because there are realistically ways for your spellcaster to avoid taking damage, such as positioning, tactics, and character builds. Concentration can and will get broken, but it happens less frequently and doesn't feel as harsh, because you likely got at least a few rounds of use out of your spell anyway. Early levels generally don't have as many sources of damage that can't be evaded with AC or a passed spell save. In BG3, you are regularly subjected to attacks that can require you to make 3 conc. saves on a hit, or 2 conc. save even if you dodge the initial attack.
Larian compensated for the increased amounts of unavoidable damage that you can take to your HP, by letting everyone eat or drink a potion as a bonus action, but there hasn't been any compensation dedicated to preventing concentration being broken yet.
