--Update--? I believe the issue was resolved.
Yes, the battery was disconnected and the device was not connected to USB. The power was completely off.
I disconnected the display ribbon cable and battery, cleaned the pins on the cable and the connector with isopropyl alcohol. Then reconnected the display ribbon cable & and battery in that order and it seems to have fixed the problem. I ran the self test and everything was a pass.
Here's a picture of the self test.
I tried measuring a 300MHz & 1GHz input sine wave and everything seems to be working just fine. The power level seems to be a bit off, from what I remember my 300MHz source was outputting but I'll look into that later. I believe there's power calibration procedures available online, right??
I have no idea what may have caused the issue. As N2MS said, maybe the TinySA Ultra was too hot from running a long time and some how things expanded such that it led to an intermittent connection.
