Reporting back on what my resolution was in case anyone searches this on google, etc.
The short: check your ground wires, disassemble the burner/pilot assembly and clean everything, reassemble, make sure all connections tight, cables including green ground tight, reset controller (put nob to lowest temp for 6+ seconds), then cycle power.
I was getting error code 5 blinks, 4 second pause. Which usually means false flame, or flame out of sequence.
I figured the issue was either with the controller itself or the flame sensor / spark rod (all in one device on this model). Usually the spark rod fails closed, which would lead the pilot light to go out after lighting. I wondered if it was possible for the flame sensor to fail shorted, leading the controller to believe there was a flame present even when one never was.
To be clear, I never had pilot flame. To further my theory, when I disconnected the spark rod I could hear ticking, leading me to believe the issue was with the spark rod.
I dis assembled the entire burner / pilot / flame sensor assembly, cleaned it, and reinstalled it. This included using a rough cloth to clean the flame rod metal.
Didn’t see any obvious cracks, etc. Checked the green ground wires and plugged all gas pipes back in. Reconnected all electrical, and it fired up.
I suspect either the flame sensor was shorted to ground (hence the false flame readout)(unlikesly, since as I mentioned no cracks etc.), or the green ground wire was finiky (most likely), or the controller is on the way out and needed to be reset a few times (second most likely). just reporting back if anyone searches this.