Zcash Flypool hashrate seems to double for short periods of time

[Lookingfordarkskys]

I have been on Flypool for a long time and seem to have very few problems and I get everything I expect but something strange is happening every few days so far. For just a couple of hours my hashrate will exactly double from an avg of 60 to 120. Happened 3 times today alone. Seems odd to me, I'm using 4 z9 mini's. Anybody seeing the same thing?