A quick e-mail to Missile Works resulted in discovering the problem (Jim explained what likely happened and what to look for). There was a short in the e-match and the current exceeded the RRC3 3 amp rated capability. The battery feed trace on the top side of the PCB that feeds the terminal block for the e-matches blew.

It's an easy repair to make, and I'm going to tackle this one but it reminded me that I need to get a current limiting resistor back in-line on this to protect the circuit. When I first built the rocket, I had a large power resistor installed (it was one I had on-hand). It was a 1 ohm large aluminum bodied resistor with mounting lugs rated at 50 watts. I started thinking about this more and wanted to calculate the proper value to use with my setup, so I made a spreadsheet that you can plug numbers into.

Note that there is an alternative wiring scheme documented in the Missile Works user manual where you run a separate pyro battery directly to the e-match and only connect the other lead to the RRC3 output negative terminals. This would be another workaround for the burned trace, but I'm not running that wiring arrangement.

My parameters are:

2-cell Lipo power (max battery V = 8.4V, min 7.5V)

MJG e-match nominal 1 ohm +/- 0.2 ohms

minimum recommended all-fire current for e-match: 1 Amp (technically it is good down to 0.6 Amps, but MJG recommends 1 amp for margin)

Max current capability of RRC3 = 3 amps

So given all this, I calculated that a 3 ohm 25 watt resistor in-line will provide protection in case of a dead short in the e-match circuit (at max battery voltage) and still provide greater than the minimum all-fire current with the lowest possible battery voltage.

These guys: https://www.amazon.com/gp/product/B07H5GBF2D/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

If anyone else wants to see what I did, or run some numbers for themselves, here is my spreadsheet:

Spreadsheet Link