Too much roasted malts in stout

I'd add a small amount of baking soda in a sampling glass to the beer and taste. If the roasted malt bitterness on your palate is a pH issue then you can maybe smooth it out some. It's at least a learning experience to give it a try.

 

There have been studies showing that the perception of bitterness actually increases with increases in pH. There's an interesting plot on slide 7 of this presentation:

https://www.asbcnet.org/events/archives/2016/proceedings/Documents/46_Driesner.pdf

 

Absolutely true for IBU's, whereby not only are more IBU's liberated at higher pH's due to higher rates of isomerization, such elivated pH liberated IBU's tend to be more rank as to their flavor. Malt acidity is different from IBU's. One can mash at pH 5.5-5.6 to control malt acidity, and then acidify post sparge and pre boil within the boil kettle to target a room temperature measured pH of 5.2 whereby to control isohumulone dissociation for smother hop bitterness.

https://www.onlinelibrary.wiley.com/doi/epdf/10.1002/j.2050-0416.2010.tb00783.x