I brewed an oatmeal stout 1.072 OG. Racked it onto a yeast cake, S-04 from a previous brew that had 1.080 OG and 1.023 FG. Started quickly and stopped suddenly at 1.033 and stayed that way for a week or so. I brewed another IPA with S-05. I racked the stout onto the S-05 cake and within 6 hours the krausen was about 3 inches high and the yeast are working again.
Before I racked it I tried stirring and bringing the temp up to 70F and no activity.
Now, what actually caused the stout to start fermenting again?
The different yeast? The big move? Luck?