Did some research here - wiped the phone and SD card and set everything back up from scratch. All was good. Restored all data and apps over a few days, still good. This morning, I reenabled SD card encryption and the reboots started within the hour.
I'm not sure why Moto has such a hard time with a basic function of SD encryption, but it's really annoying. I had issues with it on Marshmellow until one of the recent security updates fixed it where the card couldn't be accessed once encrypted.
I'm disabling encryption now to see if that solves it, hopefully I do not have to do another wipe again.
Moto needs to get their act together with this basic security function.