D4 Dice Error

Sorry new to posting about bugs, but I just had a roll of 3d4 and one of the rolls turned up a 9?

With the two exclamation marks you are telling it to make a Compounding Exploding roll, which means every die that rolls a 4 will roll again, adding the total. If it rolls another 4, it rolls again, adding again, etc. It looks like one die rolled a 4, then another 4, then a 1, for a total of 9. You can read more about the exploding dice syntax in the wiki here: <a href="https://wiki.roll20.net/Dice_Reference#Exploding_Dice" rel="nofollow">https://wiki.roll20.net/Dice_Reference#Exploding_Dice</a>