Recently many people noticed a change that showed directory viewer number vs dashboard (or stream page) vastly different.
On the twitch subreddit a response was given by flgr "viewcount lead";
"Live viewcounts (on the channel page below the live video) are finally updating much faster than they used to. We deployed a change on Friday that will update them around every 30 seconds (from 1 to 2m+ previously). We're planning to get this down further in the future (though it will take us some time). Directory viewcounts don't update quite as often so can be a little behind." - Source
Which means viewer count numbers are going to be less lagged and a little more accurate. Expect to see concurrent numbers for certain streamers lower then what they previously had due to this change.
Other note worthy effects from this polling change is the following:
- Disconnects / Small interruptions
Any issues will cause your viewer numbers to reset to zero more frequently then what it was in the past. - Playlist System / Embeds
If your channel is setup with a playlist that automatically runs when your offline, as soon as you go back online all the viewers get cut off, which makes the view counter reset. In the past with a one to two minute buffer, it just continued the count for a majority of the time.
Update 6/2/2017 - Been noticing for the past couple of days another change happened and the counters are getting more skewed.
Update 7/28/2017 - Twitch Staff lead for view counts made the following statement on r/eve.
"Also sometimes viewcounts will stop updating for some viewers. This is purely a cosmetic/client-side problem (though a very annoying one). A page refresh usually fixes that. This is a problem in the JavaScript code that polls the number, and I'm reaching out to get that fixed too." - Source
Update 10/31/2017 - Since the change over from the FLASH Player to HTML5, the new player has issues automatically starting up from offline to live states. If someone has your stream open during it being offline, and then you go online there is a good chance it wont start until the webpage or the player is restarted.
