There have been two insane difficulty spikes.

However most of the POT hashrate doesn't come from one of the listed pools (or I missed it, anyone got a clue?)

http://chainz.cryptoid.info/pot/#!extraction

So any hiccup with the majority holder will result in massive spikes...

(if you know who that "Unknown" might be let me know, I'll add it, but from the transaction history, it doesn't seem to be a regular MPOS pool)