(April 2010 15" MacBook Pro/2.66GHz/Core i7/8GB RAM [maxed out]/OS X 10.11.4)

Since I upgraded to El Cap I've had an endless run of events like this that are apparently the root cause of stuff like this. I'm almost never aware of them until long after they've happened, but every once in a while Safari slows down inexplicably and when I look... Voila! (Actually, most of the events I'm seeing are related to WindowServer, they don't correlate with the WebKit events, and don't seem to have any "visible" affect with the possible exception of causing Butler to crash.)

This happened in 10.11.2 and .3, and it continues in .4, the swap files are created at the same time as the .diag files, and ALL I'm doing when this-all happens is listening to music over AirPlay and emailing or surfing.

Is anybody else seeing similar behavior?

Edit: I haven't got any log files lying around at the moment, but I'm also experiencing (I guess I can call them) hangs that cause CPU usage spikes for a minute or two at a time.

I see far fewer of them than I do of the "microstackshot" events, and I don't see any correlation between the two types of events.

Unfortunately, I've now got one...

Hmmm... The events are "freestanding", too.

4/21/16 1:56:11.012 PM cloudd[398]: Could not create primary backing account
4/21/16 1:56:11.158 PM FileStatsAgent[2090]: Metadata.framework [Error]: couldn't get the client port
4/21/16 1:56:11.210 PM com.apple.xpc.launchd[1]: (com.apple.FileStatsAgent) Service only ran for 0 seconds. Pushing respawn out by 10 seconds.
4/21/16 1:56:17.462 PM sandboxd[191]: ([1625]) Cookie(1625) deny file-read-data /Users/artie/Library/Caches/com.apple.Safari/WebKitCache
4/21/16 1:56:21.361 PM FileStatsAgent[2091]: Metadata.framework [Error]: couldn't get the client port
4/21/16 1:58:22.295 PM MemoryStick[395]: 178 pageouts
4/21/16 1:58:32.897 PM MemoryStick[395]: 71937 pageouts
4/21/16 1:58:43.499 PM MemoryStick[395]: 28163 pageouts
4/21/16 1:59:01.328 PM MemoryStick[395]: 7 pageouts
4/21/16 1:59:22.534 PM MemoryStick[395]: 6 pageouts
4/21/16 2:00:04.142 PM tccd[388]: SecTaskLoadEntitlements failed error=22
4/21/16 2:00:04.225 PM com.apple.WebKit.WebContent[2093]: SecTaskLoadEntitlements failed error=22
4/21/16 2:00:04.226 PM com.apple.WebKit.WebContent[2093]: SecTaskLoadEntitlements failed error=22
4/21/16 2:00:04.226 PM com.apple.WebKit.WebContent[2093]: SecTaskLoadEntitlements failed error=22
4/21/16 2:00:17.455 PM sandboxd[191]: ([1625]) Cookie(1625) deny file-read-data /Users/artie/Library/Caches/com.apple.Safari/WebKitCache

Can anybody hazard even a wild guess about what would cause the activity in red? (The only apps open when it happened were Mail, Safari, and iTunes, and I wasn't even sitting in front of my deuced Mac(hina).)

Looks like it points to WebKit as the culprit/victim......restart Safari.

Thanks, but I dunno about restarting Safari.

The WebKit incident was over a minute after the pageouts, and under any circumstances, I wasn't even aware that anything was amiss until long after the fact. (I see those same WebKit entries - always in groups of three - frequently, but almost never with any side effects.)

As an experiment, I've stopped leaving eBay pages open to see if anything changes.

Edit: Nothing changed with eBay pages closed.

I've never seen the second and third Console entries before, but that's not to say that I haven't just overlooked them; the sequence accompanied a WebKit crash and the creation of a swap file.