I'm just giving you sh!t...

Yeast don't like to experiencing quick big shifts in temp. If your yeast warmed up to 65-70 and you pitched in to 80ºF wort they will be a bit gun shy.
Yeast are good for up to 5 generations, or at least thats the common thinking, So at 3 generations you should be fine. After 5 generations they will need a rest or to be replaced.