I spent most of this afternoon in my backyard wilderness where there are many bird species and also the minibeasts are gradually appearing. I had my Olympus 60mm Macro on one M1X body and Oly 300mm + MC-14 mounted on my other M1X body so that I was prepared for either insects or birds.
My main purpose was to further try out handheld Focus Stacking on both lenses. What I discovered was that instead of switching in and out of C2 (my selected Custom Mode for Focus Stacking settings) I could merely toggle the BKT button on the top plate On/Off and also I would see the reduced image area frame and the BKT icon when it was switched On.
What I also discovered, which led to some frustration until I worked out how to solve it, was that image writing to card must be set to RAW if you want the stack to combine into a final JPEG onboard camera. If it's not set to RAW, you see an error message telling you that the stack combine failed to complete, although I saw later that the full set of images were still recorded for uploading later.
I think what might have happened is that as a result of Focus Stacking and creating both RAW and JPEG files on a card, that card needs reformatting after you have set the camera to only write RAW files. Otherwise after onboard Focus Stacking, the card remains instructed for RAW + JPEG and not RAW exclusively. I may be barking up the wrong tree but being unable to ask Olympus Customer Support, this is the only reason I could find for the problem.