@dc42 I found some time to play around with this - not much but a bit.
The trailing double quote character was missing on the "fastjog" macro file that is on the machine. However, this in itself does not cause the "Homing failed" error message to appear (it may well generate other error messages but not the "Homing Failed error message).
The tool command in the homing files on the machine was indeed TO rather than T0 (the letter "O" rather than zero). But this on on it's own does not cause the "Homing Failed" error message.
There is indeed a T0 (zero) in the config.g file (it's at the end of the "Tools" section) and I can confirm that on power up, DWC shows Tool zero as highlighted.
So the sequence of heater commands when homing, was as follows.
T0 (zero from config.g)
TO (letter "O") at start of homing macro
M104 S140
M109 S140
The above commands did not cause the heater to behave in any way other than expected. That is to say, the hot end would start to heat, XYUVAB would be homed, then the system would wait for the hot end to reach 140, then the rest of the homing macro would complete.
The "Homing failed" message appeared right at the end of the homing sequence - i.e. after the second, slow homing of the Z axis. (But the axis itself shows as being homed on DWC)
Correcting the TO (letter O) and replacing it with the correct T0 (zero), and correcting the missing trailing quotes from the "fastjog" macro but using M109 instead of M116, still causes the "Homing Failed" error message to appear.
Using M116 instead of M109 does stop the "Homing Failed" message from appearing.
Both 109 and M116 perform exactly as expected with any heater errors
So this is very specific in being the use of M109 instead of M116 will cause a "Homing Failed" message to appear, but it does NOT have any impact on the operation of the heater, and the message itself appears right at the end of the homing macro (not during the heating process itself). Might it be the very last M104 S0 after that prior M109??? I'll comment that out to see if it makes any difference......
So I'm still baffled as to why the use of M109 causes a "Homing Failed" message to appear, when the heating process itself happens correctly and without any error. I double checked, having corrected the TO and the missing trailing quotes and it's definitely just the use of M109 which causes a homing failed message to appear later.
Finally, I quickly ran the pre-print home all macro "stand alone" and it ran without errors. What normally happens is that this homing macro gets called by another pre-print macro which takes care of other things like heating the bed and I've temporarily disabled the call to that pre-print homing macro. When I get chance, I'll re-enable it to try and pin down what's causing those Homing Failed" errors.
EDIT. The errors appear on DWC - I don't have a PanelDue. Oh, and in case you've forgotten, I'm running stand alone - I don't have an RPI either.