Premiere Pro and Media Encoder 2019 Not Using CPU Properly

I've been having some issues lately with Premiere Pro and Media Encoder not using CPU properly.

I'm having this issue on 2 macOS installs, Sierra 10.12.3 and High Sierra 10.13.6, the latter is a brand new install I did today.

This issue is happening on all Premiere projects I'm currently working on.

It usually goes like this, I send it to Media Encoder, hit render and it goes smootly, then, a few moments later, I send a new version to Media Encoder, hit render again and render time is 20 times more than the first time. On the last project it was 3 min vs 60 min.

When it goes smootly, Media Encoder reports normal CPU usage, when it is slow, it shows around 20~25% of usage.

Sometimes it works again after reopening Premiere and Media Encoder, sometimes only after a restart.

I also have the same issues when trying to render in and out inside Premiere.

I'm not doing anything fancy, 4K ProRes footage, Lumetri Color and a few imported titles created on After Effects.

This started happening after upgrading to CC 2019. I don't have this issue with AE, just PP and AME.

SPECS:

Intel Core i7 7700

NVIDIA GTX 970

32GB RAM

250GB Samsung 860 EVO - System

240GB Kingston UV400 - Cache

1TB Seagate Barracuda 7200RPM - Project Files

8TB Seagate Barracuda 7200RPM - Footage

macOS High Sierra 10.13.6 - Hackintosh, brand new install.