It would be helpful to copy the Console messages here to help isolate the problem.
The fire detection message should be unambiguous, although it can be triggered by anything from bright sunlight to the usual fireball generated around the laser beam while cutting. Setting the detection threshold higher usually resolves the problem.
Aaaaand the laser head may be shutting down due to thermal protection: the laser overheats while running a long project at full power. I don’t know a thermal shutdown generates an error message or just turns off, but several other folks seem to be having that problem.