An update about my issue...
After doing some exploring on you tube, some dude explained about pressing the shift key while CbB is opening a project. This enabled something called Safe Mode inside the project while it's still opening...
So, I went ahead with this procedure. It gave me the choice to open plugins manually. I avoided the Yes to all and No to all choices. So I walked through with the project about choosing the plugins. I left all plugins as they were before but cancelled the M1...
Such enabled opening the project. Then right clicking on the tracks that had the M1, I chose replace synth and chose M1 once again. Problem solved...
However, the previous M1 presets weren't rescued and I had to re-assign them. Of course I had to use my memory or try some presets again, until I'd find the suitable ones...
As a preventive measure I'm writing on a piece of paper those presents to save time and effort if this happens again, with another Korg update. Let's hope not...