Applying to a photo a preset that refers to a custom .dcp camera profile and then copying settings from that photo to a virtual copy produces incorrect results on the copy, and the Library thumbnails fail to update. Tested on LR 10.1 / Mac OS 10.15.7. Original report:
4. Take the original into Develop and apply the preset C - Kodak Portra 400 UC. Note that its Temp/Tint changes from 5050 / +5 to 5500 / -21.
5. Do Settings > Copy Settings, click Check All, then Copy. Move to the virtual copy and do Settings > Paste Settings. Note that the virtual copy's visual white balance changes but Temp/Tint remains at 5050 / +5. The original and virtual copy look different in Develop:
6. Change the WB of the virtual copy to Auto and then to As Shot. It now has Temp/Tint of 5050 / -21 (same as the original), and flipping between the original and the copy while remaining in Develop, the two images are identical.
7. Go to Library Grid view and observe that the two thumbnails still look different:
Updates to Lightroom Classic and the Lightroom Ecosystem products for Desktop, Mobile and Web were released today and contain a fix for this issue. Please refresh your Creative Cloud application and install your update when it becomes available. Thank you for your patience.