Boron flashing yellow on boot

I've had a recurring issue, not every time, but occasionally, where when I boot my boron connected to this NCD Relay board, and usb powered, it starts flashing yellow. The surefire fix has been to unplug the relay board and boot it only with usb power instead of with the power from both the relay board and usb.

Do you know if there's a fix to this?

Is it booting right into blinking yellow (DFU mode), or is it going through the sequence of blinking magenta (red and blue at the same time), then blinking yellow?

How have you connected the Boron to that board? That socket can't be used with the Boron.

It goes straight into blinking yellow. I'm using this adapter hat from NCD to be able to use the Boron with that board ->

That's not an expected behavior. The only way a device should go into blinking yellow directly is if there is no user firmware on the device. But since it works when you remove it from the shield it clearly does have user firmware.

It does appear that it's probably power related given the circumstances, but it's not clear exactly what the problem is. I'd guess maybe something to do with the rise time during power up, or something along those lines, but it's not a known problem.