The share was created when the user was created. I accidentally deleted the user, had a couple of other problems to reconnect under WIN 10 Pro and had finally to proceed with a 40 sec reset. This should normally not erase date but the private share having the same name than the deleted user shows as empty. How to recover these files?
Yes, I know but apparently corrupted the access even for the admin. I finally solved the problem by unmounting and connecting one HD to my PC. This allowed to access the data and store it on another USB drive. I then proceeded to a factory restore (yes, it take some time) and now it running again as a charm.