I am just going to throw some stuff out there since no one has replied. Maybe beers with lots of adjuncts/ non base malts, like stouts, there ends up being a lot of proteins. They can make a thick krausen that will stick around. Possibly a slow and very steady fermentation temp keeps the krausen slowly going. I just had a long krausen with a kolsch though, but I kept it around 60. I usually will swirl it for 5 seconds for a few days and it will fall after awhile. That yeast might not floc very well. It won't negatively effect the beer.
Up Next: Lawnmower Kolsch, Dry Stout
Primary: House Pale Ale, Summer Cider
Bottled: Running low. . . a little of everything