I believe it would be right coding. O_o
Even tooltip sais you cannot have disadvantage aswell.
https://baldursgate3.wiki.fextralife.com/Sneak+Attack+(Melee)
REQUIREMENTS
You have advantage, or another enemy of the target is within 1.5 m of it and you don't have disadvantage.
Aaaaand, as I said, Rag, in the most common example, you do not have disadvantage on the roll because you have an instance of both advantage (such as high ground) and disadvantage (such as being far away), and so your attack roll is made straight - i.e. not at disadvantage.
If there are five different factors that would give you disadvantage (You're at long range, and you're blinded, and you're restrained, and you're poisoned and your target is heavily obscured) and one factor that would give you advantage (your have high ground on your target), then you do *Not* have disadvantage to attack. Your attack roll is made as a normal roll, and you do *not* have disadvantage on the roll. If, by chance, the paralysed enemy you're shooting at has your friend standing next to them waving a sword at them as well, then you *CAN* apply sneak attack if you hit.
My suspicion is that the game is locking out Sneak Attack based on it reading a disadvantage factor being present, and not considering whether the roll is actually being made with disadvantage or not.
