Rainbird valve going on randomly
Today the valve went back on at 12:55pm local time. Also, while it was on, it did show valve 2 active on the display and the 25 minute countdown timer that I normally use for it, so this is 100% the controller.

I could not find any program setting or schedule that had only valve 2 going on at 12:55pm (which also is impossible according to the scheduler of the controller which works only in 15 minute intervals), so I assumed it was some kind of weird or bad programming state, especially since I finished replacing and rewiring the valve around 12:55pm on Sunday (though this may be a coincidence).

Earlier today I did a factory reset and re-programmed my nightly schedule from scratch. We'll see tomorrow whether or not that worked for sure. ;)

EDIT: it worked! Controller was in a weird state, a factory reset fixed it.