PS just a thought - try moving the M552 S1 command to the end of config.g and putting a G4 Sxxx delay command just before it, in case it's an issue with power stability or something like that.
Also, make sure that "Log any successful gcode" is not checked.
Macro is really simple:
The PanelDue is on 1.15c, should I reflash this? Sometimes it updates instantly, sometimes not.