Seems to be a mod, considering the net address. This crossbow is seemingly shown by someone with the GWM feat? Otherwise the + 15 damage does not make sense. Of course the damage would not be applied, it's a bug. Did you take the Weapon Master feat for Astarion or why can he use a heavy crossbow with proficiency? If a crit comes from 20 and 19 (so double the rate than normal?) why does the log show a crit with a roll of 13?
Generally I would not mind such a crossbow as a very rare magic weapon, if the normal TT crossbow rules would be applied (I hope they will). Ranged is a bit underpowered in the game. I would prefer a lot less magical stuff in the game but I fear it's too late for this.
