If you have a problem with darker beers and not with lagers I’d suggest it could be the yeast that you have a problem with.. If I brew a dark beer I don’t bother so much with finings as I would with a paler beer
Typically all beer contains barley, hops, yeast and water. Darker beers will contain darker roasted barley, but it’s still barley. Stouts will also contain, guess what, more dark roast barley, and sometimes oats. How are you with porridge? If ok then it’s not the oats…
Some beers – most English ales – also contain wheat, as do weissbiers. Are you ok with weissbiers? or wit beer ? Same thing.
Eliminate all of these and the only other variable is the yeast…