Hey, your doing good on trouble shooting
My bet is on the loose clean out plate as the #1 culprit. If that's loose or open, the air will bypass the coal bed and it will act just as you've described. The slid to one side or the other to lock in place. This cold spell can put a serious downer on the new side of the coal-burning-learning curve
By all means, you do need to get at least a mag thermometer. I prefer a hand held infrared thermometer as they are more accurate and give instantaneous measurements. You need this tool to assess the impact of your adjustments on the fire.
I agree that Nut is easier to learn on. It responds faster but pea will give you just as hot a fire with a good drafting chimney, just not as quickly as nut. Nut allows for bigger air channels between the coal pieces and therefore combustion will be a little quicker. Don't fuss with the fire too much. Once you get the fire to hold, make only a couple adjustment over a 12 hr period. It will take some time for the fire to adjust and settle in to show the true results of your adjustments.
That's a nice looking brick backing. It might be acting as a heat sink in this weather. I had a similar backing behind my old wood burning Defiant. It took some time - a few days - to warm up and even out. I really did suck up a lot of heat but it eventually returns it all to the room albeit slowly by radiation, not much convection. I found that if I put the back heat shield on the stove, I got more and quicker warm air convection and still had the nice radiant heat from the brick.
I do not use an MPD nor a barometric damper. The stove is well designed by combining the internally dampened (similar to the effect of an MPD) dual side/back pathway and the thermostatically controlled air inlet. Having said that, some owners do just fine with either attached to their Vigilant (older models? - look at Rewinder's avatar). I don't have nor see a need for one on the 2310. Once settled in, my Vigilant hums a long at 700* on the middle of the griddle and the stove pipe skin temp is ~170 at 6' above the stove with the draft measuring -0.1 measure at the secondary air inlet on the left side of the stove. That's seriously good draft and it's not pulling excess heat out of the house (as a baro does) or the stove, attribute that to the design of the stove's internal restricted path and the t-stat air inlet. With this amount of draft, I don't have a problem burning pea. Don't run the stove with the air control open much past half way. I run just past half and cruising at 700*, it's cracked open at ~ 1/16-1/8" with easy 14+ hr burn times on a full load. Sorry if this is redundant, you've probably already read this in the older threads on this stove.
Tell us more about your chimney. Is that triple wall air insulated or double wall rockwool insulated? What is the diameter? I does seem that it is a bit short given the proximity to the roof line and the tall nearby trees.