Earlier this year I brought in my 1963 Accutron 401 with the 214 movement to be adjusted as it was running fast. I got it back and it ran great until a couple weeks ago.
I have never seen this happen before, but it seems to be running alternately slow and then very fast. When it slows, it sometimes even comes to a stop for a second then starts up again. Not "alternately" as in it seems to run slow some days and fast on others, but rather it runs both very fast and very slow multiple times within the span of a minute. This all started after I simply set the time on it one day. I have removed the battery to make sure nothing is damaged any further and will be taking it to the matchmaker soon, but I'd like to know if anyone has experienced this before or has any idea what could be causing this strange issue?