To get around this I saved the Example sketch to disk, deleted the file Dices.ino and then opened Dices_MPU6886.iso. You will get a message about requiring that the directory name be changed, which it does for you.
You should now be able to successfully compile the sketch to the m5stick.
Scratch that, I figured it out, it was completely my error, I had the wrong "Series" selected in M5Burner. It was set to Stack-EN and once I switch it back to StickC all was well.
I must have switched that accidentally at some point. So glad I finally spotted that, such a dumb mistake.
Thank you very much for your help @ajb2k3