In the timeline, on any of the clips/events that I have colored, I right-click and export a 3D LUT. This defaults to a .cube. I then import that via the color settings and that is now part of the color transform menu selection.
Are you sure there aren’t multiple transforms being applied? That can happen sometimes when MC want to “auto-apply” transforms if it sees something in the metadata fields. Bring up the Color Transform column in the bin and see what it being applied. If more than one transform, the order of the transforms can radially change the way an image is being processed and that can be changed in the source settings/color transform window by dragging and dropping the “LUT”.
I did a webinar for Moviola that covers a lot of this and be seen here (for a rental fee): https://moviola.com/webinars/4k-with-avid-blackmagic-design/
If you want to send me your LUT I can import it and see if I am seeing the same artifacting you are on my footage.
michael[at]24p[dot]com
Michael