Google PageSpeed Insights last update .. what really happened !?

[yonited]

As a newbie, I did some really hard work with my website and although it is a crowdy images website as it is about mobile apps I could get a pretty good score on PageSpeed Insights by Google with a desktop score around 90+ and mobile score 80+ using some free WordPress plugins like speed ninja and some premium plugins like wprocket , I also took care with images optimization before uploading them.

after the last update although my desktop score is the same my mobile score went to the ground which is really bad as most of my visitors are from Android mobiles and iPhones, so what really happened in that update and why it did ruin my score