I’ve encountered this bug four times so far, each time trying to the Flawless Archaeologist achievement.
In a room with a central pillar, you have a Creeping Death patrolling around the pillar in a clockwise faction. This room have 4 corridors branching off it – the one you enter from, two that leads to wall switches, and the exit where the Knot of Isis (ground plate) is.
However, when rounding the last wall right before this room, the Creeping Death instantly stop moving as soon as it appears. This makes it impossible to advance in the labyrinth without dying, and with it goes any chance of doing said achievement.
For anyone experiencing this bug, a workaround is to attack the mummy at range and then run back to the previous Knot of Isis floor panel just around the corner; the mummy has a very small reset distance and will only chase you to the end of the hall before returning to it’s patrol. This has the same effect as dying or re-entering the instance in that it will force the mummy to begin moving again. You can repeat this process as many times as necessary. Since entering combat causes you to drop your torch, I suggest preemptively dropping it at the bend in the hallway such that that both sides are illuminated.