Thanks, Andreas. Yes, there are a lot of reports of freezes like I'm experiencing out there on the net. At one point last year there were many reports posted and over 15,000 "I also have this problem" upvotes of them on Apple's own forums of this very issue. Apple has since scrubbed all of them from the internet. It seems something fishy is going on, Apple obviously knows what it is but they've refused to comment in every single instance.
I finally contacted Apple support on the phone and spoke to a rep and, after contacting engineering, he emailed me telling me to boot into Recovery Mode and run the following command in Terminal, which I did:
Interestingly, in the email he copied and pasted from engineering to me, it included the final step, which read,
"The HDCP content should play back normally" - obviously provided by engineers, because the rep hadn't said anything regarding "HDCP".
This would seem to indicate that it could be a "High-bandwidth Digital Content Protection" playback related bug. I'm running Safari most of the time and usually streaming Youtube audio, so I started to think this might be the culprit. After running the above command in Oct of last year (2018), I got one more freeze that same day but then no more until about two weeks ago.
(Same solution also posted here, which I've since found:
If I had to guess I want to say that it might have to do with having lots of Safari windows and tabs open (bad habit of mine) and playing video content (sports streams, Netflix, streaming YT audio, etc).
Anyway, hope this helps in case anyone else runs in to this issue thinking it is BTT. I'm still enjoying BTT and use it all the time. Thanks again!