Well well well... I could isolate one of the RGWs and downgrade the packages to the version that I know was working fine. Then I forced Windows network traffic to go through this RGWs (entry in hosts file) and it appears that the Ceph version is not the cause. Creating a folder still results in showing 4 folders, with actually none created.
What I don't understand is why this is now happening as I don't remember ever encountering this issue before, when I made all my tests of the rclone mount in September (Rclone download) and the windows user attached to the rclone mount service was already the .\SYSTEM user.
When mounting from the CLI with no user privileges elevation (Windows+R + 'cmd') I can create a folder with no issues (virtually as the folder is not actually created until a file is dropped in it) and it doesn't turn into 4 folders being created (or not created actually).
When mounting from the CLI with Administrator privileges elevation ('cmd' run as Administrator) then it doesn't work and a folder creation turns into 4 folders... Same as if the mount was started by the service under the .\SYSTEM account.
I'm not sure how to solve this. Should I use a specific user to run the windows service?
Frédéric.