Krausen is Back After 14 Days?

I Brewed Revvy's Leffe clone recipe using WLP530 14 days ago. Made a 1.5 liter starter and fermented at 64* for 7 days. Days 2-4 were pretty active with krausen going into the airlock. Things seemed to calm down so I ramped to 68* on days 8 and 9. Things definetly slowed down with maybe 1 airlock bubble every 30 seconds and no visible movement inside the carboy. Last night I checked on it and the ferment was full force, almost needing a blow off tube again. Looking inside I could see the violent convection of the ferment. What gives? Could it have been the high mash temp at 158*?

Belgian yeast are crazy. I'd go with that.

Could be top-cropping flocculation...as they finish, they clump together and rise to the top, but that wouldn't be "full force blow-off" fermentation.

Did you take a gravity reading or disturb the beer in any way?

When this has happened to me (three times) it was when I mashed too high (due to faulty temp probe) *and* used a low attenuating yeast. The timing and full-blow nature of the fermentation restarts happened pretty much as you describe. Haven't noticed it after mash temp problem was corrected.

I just had a "return of the krausen" experience with Safbrew S-33 in a small beer. 13 days in the beer, which had partially cleared, clouded up again and began to grow a new krausen. Gravity showed it to be a tad short of my expected final. My conclusion is that, especially for some yeasts, "life don't clickety-clack down a straight line track" (train analogy).