Hi,
I must say I am not really a fan of reading in R3D files into Nuke, because of the many combinations possible and therefore the many ways that this can go wrong.
I would rather recommend to convert the R3D footage to ACES 2065-1 EXR files with Resolve or RedCine-X PRO and use these in Nuke.
I loaded the EXRs vom Resolve and RedCine-X PRO into Nuke and then loaded the 3RD into Nuke 12.2v2 as well.
I had to set the read node to the following settings to get a match:
(I also had to click Load Settings from RMD.)
I hope this helps.
Best regards
Daniel