I also posted this on the Sony forum and received a solving answer from MarkF…
“If you are using (I believe) ver 10.3 or beyond in FCPX, it will partly read the camera metadata and apply the Sony conversion lut automatically to your footage. You can check this by selecting the clip in the timeline and then looking at the inspector window. In the drop down “metadata view” tab – choose “settings” and then see what shows up on the log processing line (it’ll likely be Sony S-log3/S-gamut3 cine). If you change this to “none”, you’ll see your original s log footage again.
To take off the automatically applied lut to all clips, simply select them all in the clip gallery, and then choose “none” again in the log processing area of the inspector window.
Hoping this will get changed in an update eventually – or even better, allow you to use your own custom imported luts instead of the 8 options they currently have.”