Nice bug, i agree. You need to look up why the game sees you at a DA
Also, the whole sneak attack mechanic is weird.
Normally you can sneak attack ONCE...cause you are not sneaked anymore after that. So the first attack out of stealth is a sneak attack,period. Our rougues can sneak attack every round when they have an advantage.
I usually see a sneak attack as something that is carefull planned and executed and does a LOT of damage because of that. NOT something you can do in a melee, advantage or no. Our toons do not stand still during melee (otherwise no attack would really miss) thats just graphical.
A little bonus damage for every attack for chars able to sneak attack i would understand. Having an enemy engaged with another gives you a little more time to hit weak spots. Not time enough to launch a debilitating killing strike to a vital point that moves around.
Thats how i see it at least. No idea how 5e explains it.