Hey there! It's a great question but I don't know the specifics of the explanation, unfortunately. At first glance (I'm literally just hearing about this from you) my assumption is that our RED support was more robust and stable in After Effects, which is why Premiere Pro might be suffering right now. We have a Premiere Pro beta board that our engineering team checks pretty regularly, have you tried posting here?
In the meantime, I can talk to our formats engineers and get a ticket filed on this if they don't have one already. Sorry I don't have a more definite explanation, but I'm happy to advocate for you here on this end!