A measurement of Vcc would also be useful, and how it changes.
Maybe also touch D109 - I expect it will be getting hot as Vcc goes up above 3.3V.
I'm wondering if you have a temperature-dependent issue that causes the 5V supply to get shorted to Vdd, pulling Vdd up and Vcc down.
Maybe also take a resistance measurement (with power off) between Vdd and Vcc.
?
When you said you could reproduce the problem by trying to attach the terminal, did it happen when you connected the cable, or when you hit enter in the terminal window to bring up the menu?
