OK, I guess it's just my watery body blocking the signal
Cross-body Interference
A little known fact about Bluetooth is that the radio signals do not go through your body very well. This is because Bluetooth's radio frequency is blocked by water, and the human body is made up of mostly water. If you keep your cell phone in your pocket and your headset in your opposite ear, then it is possible the connection may be weak, which can cause some interference issues. Many cell phone manufacturers are aware of this issue and have attempted to compensate by boosting the power of the Bluetooth radio.
reference -
What Are Some Signal Interference Issues for the Bluetooth Technology? | Chron.com
Thinking back on days that didn't have issues, that was when most of my rides commuting and I'd wear baggie shorts with the phone in a front pocket. Now that I'm working out of a home office, most rides are in a kit and the phone is in the jersey pocket. Still oddly, some days are better than others, maybe the good-reception days are a warning that I'm getting dehydrated (ha)