Premiere Pro 15.4.3 - Create Proxy function not working properly

I'm working on a TV show and am using an approved Premiere version (15.4.3) as well as the same version of Media Encoder. I'm on a 2013 Mac Pro OS 12.6.3. Things have been working perfectly up until the other week when this problem has begun; I have not changed anything in my workflow nor have I updated any programs or OS.

When I select my footage and "Create Proxies" I'll select the preset I want to use and my destination, but when I hit "OK" it will take up to several minutes to send to Media Encoder. And then finally when the clips do show up, some of them (typically the longest clips) have different presets selected compared to what I chose in Premiere. When Media Encoder begins transcoding, the ones with the different presets will fail and give me an error. If I try to change the preset within Media Encoder to my preset, it still gives me an error.

This has been very frustrating and after much searching I haven't found anyone that has dealt with a similar issue. I've re-started my programs, my computer, re-installed Premiere and Media Encoder, but ultimately nothing has helped aside from trying again and again until for no discernable reason it suddenly works. I've repeated this process for several batches of footage now and any help would be greatly appreciated!