So, the 'view over two browsers' happened again. Unfortunately I wrote the gcode down wrong you told me to enter... I wrote M112 (emergency stop)... which isn't at all what I should have typed in. So, after that I tried the M122, but it had nothing to report.
Also note, that I'd been logging in from multiple browsers (on my PC and phone) pretty constantly for the past half hour testing stuff and this didn't happen. Then, it did.
However, the initial bug was, I logged into the DWC from my PC (had been logged in on my phone), it asked for my password (which was weird, since I had just been using it a few minutes earlier, then closed chrome), and after entering it (possibly wrong), the whole machine reset and quit. Luckily I was only 10 minutes into a print this time.
I'll continue to try and repro this and enter the right gcode next time...