Started using the Caliban sword, with +200 DPS.
As soon as i equiped it, myself and party members did only 1 damage max, regardless of ability or equipment.
Just to be on the safe side, repaired the game, reloaded a much older save, and got back to the current one. The damage from all abilities is now close to 40, but only with this particular sword. With my next best weapon, the values are normal.