Hughe gaps on pageviews

hello! maybe someone has an idea, whats wrong here…
i made an overall statistic from our pageviews. and there is a hughe gap between last year and this year (Jan-May 2015 and Jan-May 2016). does some has the same Problem?
Also there is a strange thing in pageviews and unique pageviews. the pageviews went down, and the unique pageviews up?!

Would be great if someone is able to help me :wink:

thx! Cheers