The big question seems to be if your machine uses a spindle or a trim router. A lot of us have LongMills with a trim router that you have to manually turn on/off and set the speed manually.
As this is the gSender category I won’t make any assumptions about your machine. If you do have a spindle then this might be a bug. Can you tell us what kind of machine you have or confirm that you do have a spindle that uses M3, M4, and M5 to control with S for speed.
Did you mean M3, M4, and M5? M6 is tool change.