Ring-modulated sound on playback when using Elastic Audio varispeed

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Hoping that someone might be able to help me with a problem that’s been bugging me for a while! I have a few sessions where I have used elastic audio with varispeed to slow down/speed up recordings ala tape varispeed. I've had an issue where about 2/3 through a song, tracks will start playing back with a distorted/ring-modulated sound.

I've tried trashing preferences/restarting many times. I've adjusted I/O buffer size and disk playback cache size many times. I've tried using Real-Time processing and Rendered processing for Elastic Audio. I've tried unplugging/replugging the firewire cable/adapters connecting interface. I've noticed it affecting tracks with and without plugins.

I have not noticed this problem in sessions that don't use elastic audio. In the sessions that do have elastic audio tracks, the problem doesn't seem to affect tracks that are playing back at the recorded speed. I'm using elastic audio to varispeed slow/speed up instrumental tracks so they're easier to sing to. So for instance the vocals are playing back at recorded speed and aren't effect by this ring-modulated sound.

I also only notice it when I'm listening through the song from the beginning, then always around 2/3 into the song I'll notice, for instance, the bass guitar has this distorted sound. Then if I stop playback and start it from another point in the session, the problem goes away.

I can also momentarily stop the problem by changing the i/o buffer size, but eventually it just happens again. Has been going on for months now and is very frustrating! I’m about to try uninstalling and reinstalling Pro Tools 2018.7 to see if that helps. I found some other threads mentioning a distorted/ring-modulated sound, but none seemed to be directly tied to elastic audio like my problem is…

Here’s my setup info:
Mac mini 2018, 3.6 GHz Intel Core i3, 32gb RAM, mac OS 10.14.6
Digi002r, connected through Firewire-Thunderbolt and Thunderbolt 2-3 dongles
Pro Tools 2018.7
Using Lacie 2tb USB hardrive as record drive