Search console has some solid data to help you understand what happened to your site during the June 6th update.
Fire up search console and....
- select the impressions tab only
- select the date range and switch to the compare tab
- Enter June 6th to June 13th and compare it with the previous 7 day period (May 23 to May 30)
- Switch to the pages tab
- Sort the "difference" column so that the pages with the biggest loss of impressions float to the top
You can then select any page you want to evaluate and then switch back to the queries tab for that page to see what happened to your keywords for that page. DO NOT be alarmed if suddenly some of your keywords get no impressions for that page, you probably rank for them on a different page, perhaps even more highly, though you will have lost traffic for the query on that page.
So what happened?
I can't speak for all sites but on my site the keyword groupings were tightened up. I have retained all keywords associated with my pages which had a decent CTR but lost most that had low CTR and low avg rank. Overall I now have a net gain in CTR and a net gain in avg position but a loss in impressions and clicks.
In some cases my impressions were cut by 50% on some pages, they ranked for 800+ keywords but now rank for just 200. On those pages, however, the metrics for the remaining impressions are much better resulting in a higher avg CTR and higher avg rank for the page. I would think this should please advertisers.
As for the lost impressions, in many cases I still get the impressions for those keywords on other pages more suited to that keyword. What was lost was the "sorta related" keywords I ranked for but didn't cover very well. No one page can cover them all and it appears Google has simply tightened their results by restricting my pages to highly performing keywords only.
Page titles just got more important, you really need to convey what the user can expect to find and think about what they are looking for first. If you page doesn't perform for any given keyword expect to lose exposure for it more harshly since the update. My best pages lost half their impressions and half their keywords but it was all of the sorta related stuff that was lost, not the target keywords. There is nothing to fix on page, this is a change which was good for the user.
Note: Some keywords were not lost completely, they were restricted to one or two pages in cases where 2 or more pages used to get impressions for them(multi-result serps). The core update and the multi-page result update were strongly similar.