I think you uncovered a defect in the Macro processing that I was able to recreate. It is legal for the same event to trigger multiple macros. I added a second macro that trips when my F03 ON (your M01 ON equivalent) X10 signal is sent. This macro turns on an Insteon device and works fine when run alone. When I activate the If F03 ON Then F04 ON macro, not only does the second part of the F04 ON (your A01 ON equivalent) not get sent, my second macro that turns on an Insteon device does not run. Putting the two symptoms together, I’m guessing that the macro processing handling the Then X10 ON runs into a problem and traps/abends between the sending of the A1 message and the A ON message, ending the processing associated with the original trigger condition, M01 ON in your case. That is only a guess as to what is happening but there is a problem of some kind for sure. Lots of variables that might affect an Insteon action (ie my mistakes) but specifying an X10 action is about as simple as they come. Particularly when a Timer X10 action works and the same Macro X10 action does not.
SHN will review the forum posts that came in over the weekend. Probably even post some conclusions about what we have encountered but that could take a few days. If it really is critical I would call the support number Monday. They are really interested in resolving any problems found in EZSrve. I found a Macro display problem a few weeks ago which they diagnosed and corrected in very short order. SHN is working on the next image and may be able to incorporate a fix for this problem in that image.
Thanks for all the testing you have done. I feel better about a conclusion when more than one person is seeing the same thing.