One more further refinement...
I just did another Factory Reset in anticipation of the new T-Mo Oreo update - the one that fixes the issues from the previous update halted on 5/3.
This time around, with nothing but the baseline Samsung and Google software installed, and absolutely no data or settings migrated from the previous install (the only way I roll), I have isolated this issue, for my phone, down to just Bluetooth. I discovered this before the update. But since the update, there is no change.
Previously, I needed to turn off Location Services b/c I had set up SmartLock based on location - my home. This time, no settings were made following the reset, and it's purely Bluetooth at the center of this issue.
BT off, everything works perfectly. When I turn it on, all of the issues described above are in play. When I turn off BT again and reset, I am back to everything working fine. Just can't use BT.
*Edit* - If I am away from home, all is well. If I am within my house, the issues arise. Turning BT off, fixes it.
Still, I have no idea if it's Samsung or Google software, or Samsung hardware to blame. I called Samsung to get a replacement phone and their process requires that I send my phone in for "servicing". No way. T-Mo will replace it, but the Rep said that they can't vouch for the condition of the phone they will send to me as it's a refurb.
So, like my Pixel XL before this, I'll just hang with an expensive phone that has issues no one can fix.