Thank you Allan.
SetupRST.exe upgraded my SATA RAID controller driver version and "Intel Rapid Storage Technology" GUI to latest version successfully (12.9.0.1001), with no data loss, keeping the Acceleration as "maximized".
It fixed my problem. After rebooting, it does not fall back to enhanced anymore, nor does it any "transitioning".
One thing I noticed is that my "Intel Control Center" no longer displays any Intel functionality available, i.e., the "Intel Rapid Storage Technology" is no longer available from the Control Center, so I uninstalled the Control Center, as it became redundant.
Good support.
Best regards.