UFO distress signal bug.

[cerebrawl]

The distress signal is only supposed to start after you've been revealed, however on my latest UFO mission there was an ADVENT turret within sightrange, which started the countdown immediately upon mission start, without revealing me(I wasn't in its detection radius, just in sight range). Possibly something about the check for wether we're seen being run before the mission start concealment has been applied.

[TyreT]

I think I had a similiar encounter with a turret on mission start but it wasn't at an ufo.
From what I saw, the turret detects your squad BEFORE it gains the mission-start-concealment(the turret activates cutscene/event triggered).
After that, the mission-start-concealment gets applied to your full squad, so the turret looses sight of them.

This might not only affect the timer-start as you noticed, but also enemy behavior(alert level?) and the reinforcement-countdown(since you where kind-of discovered).

[tracktwo]

Yes, this is a bug, but I think it's a base XCOM2 bug (although probably more rare due to smaller squad sizes). If you start within sight range of a turret it'll activate before you enter concealment, which will start things like the UFO timer or (hidden) reinforcement timer.