So my test character (Testes) was just a copy of um… Chauncey with a different token/portrait.
I turned Testes into a barbarian by dragging the barbarian class from the compendium onto his character sheet (thus removing bard as the class). I got pop-ups for choosing instinct then dragon colour when choosing dragon instinct. Unlike Rock the rage effect from Testes’ action tab did not have updated text indicating it was anything other than “normal” rage (i.e. it didn’t mention acid damage or increase the rage damage from 2 to 4), however when Testes applied that rage effect to himself then did damage it correctly added 4 acid damage to his strikes.
I made a duplicate of Rock named… New Rock and did the same deal (drag barbarian out of compendium, repick instinct, repick dragon colour) and voila, New Rock does acid damage on hit. The rage effect on New Rock’s actions tab also does not have updated text regarding acid damage and increase in damage amount.
I’m guessing this was a pathmuncher import problem.
P.S. While raging the game is incorrectly not decrementing the barbarian’s AC by 1.