It sounds like a bug...I'd report it.
I do disagree with "With the limit of one sneak attack per round and a very limited set of conditions where it can be used" - it is exceptionally easy to SA, you can even do it at range (which I think is already hard to justify from a logic perspective as 'precision damage' due to distraction). All you need is a party member attacking the same foe. And having it apply to every attack would be overpowered. Martial classes have limits - paladins can only smite while they have spell slots (at low level these go quickly), and are then weaker damager dealers than a regular fighter, all things being equal. Fighters have 1 action surge (at low levels) and by end game 3/4 attacks per round (excluding haste) - but they are *the* martial experts, its all they can do. They have little outside of combat. Allowing rogues to add 5d6 or more on *every* attack (ranged or melee) would be unreasonable in terms of balance. Clearly the designers of 5e agreed. The problem is that Larian has broken a lot of class uniqueness/scaling by ignoring rules left, right and centre. I think rogues are already very well equipped to support combat - I used Astarion and he dealt huge amounts of damage and could also do neat things like bonus disengage, hide, high mobility etc.
