I am working on a Mac, OS 10.12.5, AE C2018 and Premiere CC 2017.
I am trying to render out QTs from AE (and Premier) using the Avid DNxHD codec, but it no longer appears as an option. I know the Avid codec is installed because I can import these QTs and I can export Avid DNxHD QTs from Apple QT Player 7 (Pro). But for some reason, when I go to render and export from either AE or Premier, I don't have this option. Instead I get something called "DNxHR/DNxHD" and A number of Avid options, but not the one I need or used to have. I have tried a number of things, but each time, the Avid editor I was working with would have to import these QTs differently and it would slo the process down.
The AE team updated the DNxHD stuff to be more modern and according to Avid's newer standards, but not all of Avid's software has caught up yet.
I don't know the right answer for what your needs are. You have a couple of options though.
You could set up a watch folder for an older version of Adobe Media Encoder to take whatever you render out of AE and make the kind of Avid DNxHD you're used to making.
Or you could do some more testing and find a newer version way that works better.