If this is something Larian is already doing, then I'm dumb and feel free to ignore this post.
Some attack types can deal multiple types of damage, such as Flame Strike dealing both Fire and Radiant damage. Many enemy attacks also can deal both physical damage and another type like fire and poison.
Solasta, when it does its damage calculations for mixed damage types, makes a fundamental mistake. It does properly check each damage type against the target's resistances and applies damage reduction or immunity, however, it treats those damage types as two separate attacks, which means, for instance, that one attack could force two concentration checks on a caster, or one attack could knock a character to 0 HP and then they automatically fail a death saving throw.
What Solasta should have done after the code for checking damage reduction finishes, is to then combine the raw numbers back into one total damage number, and that would be used. The game could still display the separate damage types popping up over enemy's heads and in the log, but it should be considered one number elsewhere for game balance purposes.
Thanks.
