If you are all in the mood for a little bit of Soviet era horology, then I'd like to introduce today's 404 club fixer upper.
A Raketa 2609.HA based Sekonda, complete with the obligatory USSR marking on the bottom of the dial.
The gold plated case (stamped AU9) and the near indestructible Raketa movement make these little Sekondas rather pleasing and rewarding pieces to resurrect.
I think it too enjoyed its well earned service and good scrub down, as it is now sitting at >270 degrees, beat error around 0.1ms and somewhere around +30 sec per day without me adjusting anything. It is still sporting the original high dome crystal, which took a good polish and save for a few tiny blemishes looks almost new
One other great thing about these (I have a couple of similar examples) is the dial. It is both easily readable, and classically elegant at the same time. A station clock for the wrist. Maybe the 1970s weren't completely devoid of taste after all.
I cleaned it by soaking in Home Depot naptha and pegging by hand, 2 rinses. Demagnetized the whole thing, as well. I'll dig back in with both suggestions and report back any findings.
Enjoying the process.
Always hard so make a guess... Anyway, I think the problem is on the dial side, i.e. the dial train (cannon pinion, minute wheel, hour wheel, intermediate wheel). Could it be that the clutch wheel doesn't disengage properly from the intermediate wheel that drives the minute wheel when you set the time? If so the intermediate wheel may bind up the minute wheel making things slow down and then stop. Well, just guessing. Anyway, I'd check the dial train (motion works) and the keyless works. I think your idea of removing the cannon pinion to see if it solves the problem is a good idea. If it doesn't help you'll know for sure the problem is with the train of wheels or the escapement.
Good luck and let us know of any progress or any new observations.