I do apologise, @ulrich, as I posted the above I had already developed the sub-macro more with more commands, and, sod’s law, the RUN error hasn’t happened since.
It did happen several times each time I played the macro. I later added “(Sometimes)” to my first post because for the first time it didn’t happen (after I added more commands). And today it still hasn’t happened again.
So I don’t know what you want to do with this thread. I know how frustrating it is to receive reports that end up a dead-end. Apologies again.
Feel free to remove this or leave it up in case someone else encounters it.