Links and PBN
This update was spotted more by the tools, than on webmaster forums. However, it was discussed on black hat forums. It seems to target links, mostly from PBNs.
There was a small update spotted both by webmasters and the tools. SERP fluctuations have been more pronounced than usual, but not alarming nevertheless.
Mobile interstitials penalty
Google started penalizing mobile websites that are using interstitials (ads that block main content when accessing the website).