during a 20+ mephit fight continually respawning, i had lots of opportunity to test this myself with Astarion

The spawned young mud mephits didn't do anything most of the fight (glitch, not really part of this thread) giving me lots of tests without the mob or myself moving (at least 40 successful sneak attacks)

the tooltip says: melee sneak attack: 1d4+3+1d6 (weapon+dex+sneak attack)

issues found:
- sometimes sneak attack wouldn't even register
----it would just do the 1d4+3 damage
----this would occure even without the mob moving or my ally moving between rounds and last round sneak attack did roll the d6 correctly (well, damage wasn't, but the registering of sneak attack conditions was what worked, see next comment)
---- most of the time though, sneak attack would register (probably ~80% of the time it would work)
- when sneak attack did register it did not calculate the damage correctly
---- it would always leave off the 1d4+3
---- i see some comments on this thread mentioning that it would list as a 2nd line item, but no, it did not list or the mob health would not move accordingly
---- the damage total health loss on the mob would be 2 or 3 damage somtimes, which is not even possible with a 1d4+3 dagger modifier (and no resistance, at least not listed in the tooltip or monster manual)


so, conclusion, sneak attack does not work (as the thread title states)