After two different users mentioning problems with the laser today, I inspected it and found the mirrors to be severely out of alignment - to the point where the (red) guide laser was not visible, and the top part of the cutting head being hot, indicating a portion of the (invisible) cutting beam might be hitting the inside of the housing.
Due to the risk of damage to the laser and/or its users, I’ve locked-out the laser cutter.
I did this by disconnecting the leads to the switch that energizes its main power contactor, cutting power to both the laser and drive motors. The disconnected leads are behind the door shown in attached image.
Do not reverse this lock-out. The severity of the problems and the fact they’ve returned so quickly mean this requires the attention of an experienced laser technician.
There are probably some fasteners that have come loose and need be re-installed with loctite. We also likely have worn-out belts and/or pulleys, causing one side of the the gantry to slip. But these are only educated guesses.
Seriously, do not try to repair this machine yourselves.