Got it. I looked at the postprocessor in CamBam and it showed the Start and end cuts were empty.
Strange, I think you have made a mismatch somewhere .. I just load and install it and the M3 and M5 are present in start cut and end cut
(but must not be set in the start and stop spindle, both must stay empty)
Note that when a post processor is selected as default (it appears with a green arrow), that not necessary means that it will by used be your project.
If another post processor is selected in the post processor property of the machining folder, it will replace the one selected as default. The PP property in the machining folder must be empty
(delete any name that can be here, even the word 'default') or select the LinuxCNC_Laser PP to be sure it is used.