Google started rolling out a penalty to punish aggressive interstitials and pop-ups that might damage the mobile user experience.
Some of these panels disappeared around December 15.
Just more than a year after the original "mobile friendly" update, Google rolled out another ranking signal boost to benefit mobile-friendly sites on mobile search.
Since the majority of sites we track are already mobile-friendly, it's likely the impact of the latest update was small.
They suggested the new Penguin is now real-time and baked into the "core" algorithm.
Initial impact assessments were small, but it was later revealed that the Penguin 4.0 rollout was unusually long and multi-phase (see September 27th and October 6th).