I am starting to think that my board may be faulty in some way…
I didn’t really think about it before, but I can also only reliably get a connection over the USB to serial if the 12v barrel jack is plugged in.
The LED turns on with just usb, but it is much dimmer, and while I detect the serial adapter, I cannot get in.
Plugging in the barrel jack instantly causes the device to boot.
Removing power also causes the LED to very slowly dim over time rather than immediately turn off as I would expect it to.