So, my recollection of sneak attack when I played in December... whenever I connected with a sneak attack there would be two damage numbers floating by. I assumed at the time that one was the weapon damage and the other was the sneak attack damage.
Is it possible you attacked with dual wield?
There is (was?) a toggle on lower left side to attack with both weapons, this was by default on. That would explain the two damage numbers.
And IF it was the sneak attack portion, then ... meh ... I would prefer actually rolling a certain number of dice, not just one and then multiply it with a number.
Which again leads me to wonder, if Larian does this in purpose because they do not understand what 5d6 means, or do they want a flat distribution? Which would mean more variation than a Gaussian distribution (I hope I use the term variation in the correct mathematical sense here).
Anyway, it very much seems that you are correct @dwig
