WordPress Performance Issue?

Just wanted to share a mysterious trend reported for my sites by Google Webmaster Tools, and ask if anyone else is seeing the same pattern. It looks like it’s related to the WordPress 4.4 update, but I’m not 100% sure, so putting the data out there in hopes that others can help shed some light on the issue..

Performance is important. When a site suddenly takes twice as long to load, that could negatively impact its search engine ratings.

From what I can tell, all of my WordPress sites are loading slower across the board, at least for Googlebot. Up until around the beginning of December, most of my WP-powered sites were averaging around 250ms load time for Googlebot. Then suddenly on around the 8th of December, the average load time more than doubled, averaging a little over 500ms for most sites. Here are a few representative screenshots from Google Webmaster Tools:

[ Google Webmaster Tools: WP-Mix.com ][ Google Webmaster Tools: PerishablePress.com ][ Google Webmaster Tools: WP-Tao.com ][ Google Webmaster Tools: eChunks.com ][ Google Webmaster Tools: htaccessbook.com ][ Google Webmaster Tools: Plugin-Planet.com ][ Google Webmaster Tools: DigWP.com ]

Some of these graphs show the pattern more clearly than others, but the trend is unmistakable: around the beginning of December, WordPress sites require around twice as long to load. I wish I would have taken screenshots about three weeks ago, as the sudden “jump” in load time was much more pronounced and clearly distinguished.

Is it the WordPress?

The thing is, I’ve not made any significant changes that would affect all of my WP sites at the same time, except for updating WordPress to the latest version, 4.4 “Clifford” on December 8th, 2015. So basically my hypothesis is that WordPress 4.4 takes around twice as long to load on my server, according to Google.

To serve as a baseline for comparison, here are the data for one of my sites that is not running WordPress:

[ Google Webmaster Tools: Monzilla Media ]

Notice that, apart from the outlier data, the load-time performance remains consistently low throughout the entire time duration. No sudden jump after the beginning of December. This points to the issue being related to the WordPress update, in my opinion.

So is anyone else seeing similar data? Any alternate hypotheses besides it being WordPress? If not, what major changes were introduced in WP 4.4 that may account for the sudden jump in load time? Couldn’t be the new REST API stuff, could it?

To be crystal clear: I’m just hypothesizing slash thinking out loud on this one.. NOT saying for sure it’s anything this or that, just pointing out what I’m seeing in the data, and trying to make sense of it, in order to find a solution. As mentioned above, a doubling of load time is not a good thing.

Any insight is appreciated.

Update: Read the thrilling conclusion to this WordPress-performance mystery!