Those gray halos on the edges of green and purple areas are from the Defringing lens-corrections area, so check your Defringing settings in ACR for the camera you’re using.
The Defringing function can’t tell the difference between purple and green halos caused by lens problems and purple and green edges of the subjects, themselves, so you have to be careful with it and probably shouldn’t Defringing on by default.
The Defringing slider of the Adjustment Brush can be used to reverse extra defringing that shouldn’t have occurred like you’ve pictured, or the Adjustment Brush with a positive Defringing amount can be used to reduce fringed areas visibility if you don’t want to use the automatic Defringing sliders.
OMG! Thank you so much! Strange, because this was my first thought to be the culprit but I didn't follow up. I guess I have to repeat the basics in physics and chromatic aberration...
I can’t explain why it’s only happening for DNGs compared to CR2 files if both are newly imported, unless LR has separate default settings for native-raw vs DNG-raw files for a particular camera.