Not sure if these were just one-time glitches or desync issues, but I have done the dungeons several times without problem. In priory, the first boss was on the stairs so the beam was at an angle and clipping, and appeared to be going up the stairs, so I went to what seemed to be a safe area somewhere behind the boss at the bottom of the stairs, but got one shot by the spear. When I looked at a log, the boss was definitely facing another direction the whole time.
In workshop, on one run I kept failing the bot steam vent maze because the bot would see me but my character was not in any of the sight rings. I have not had issues with completing this in the past. I even dismissed my pets in case it was an issue although it hasn’t been before.
Possibly not considered a bug, but the visual of the frontal on the first boss in Theater of Pain does not extend the full range of the actual spell effect. You cannot stand in what appears to be the safe area outside the visual.