Sightless watcher often gives me the option to only choose between two cards instead of three. This happens often, but not every game.
I imagine that this is an actual bug unless there’s some mechanic that I don’t know about.
Kind regards
Whether or not it is an actual bug depends on how many distinct minions were left in your undrawn deck at the time.
There is a known bug with Slightless Watcher that was introduced when a new rule was created to prevent discover cards from creating a copy of themself. It seems that for Slightless Watcher, the effect is that if one of the cards chosen in the second Slightless Watcher in your deck, it is simply not shown.
If you have at least three different other minions in your deck, then that choice should be rerolled, not removed.
If you don’t have those three other options, then this would not be a bug. The game can’t offer cards that are not there.