XPC connection was invalidated

I have the same problem, both that message as well as the xpcproxy process churning away at 500%. Except mine only happens when I have Lightroom open. When I close Lightroom, the message stops printing to the console, xpcproxy disappears, and my load average returns to baseline.

I wish I had to explanation as to why, but I just installed El Capitan today, and haven't tracked the issue down yet.

Chiming in - same problem here, lots of "Spotlight[PID]: XPC connection was invalidated" spamming the console as I type into spotlight. Also I notice that certain apps that I'm trying to launch will momentarily "flash" into the results and then immediately disappear. Really frustrating & annoying. I've done everything I can to fix... tried deleting spotlight indexes, rebuilding, adding disk to Privacy tab then removing etc etc. El Cap 10.11.1 on a Mac Mini.

I'm receiving the same message on my Mini. It seem to coincide with updating to El Cap 10.11.6 the other day.
I found these messages while trying to track down some weird behavior IE: at the top of the hour, or a minute or so after, my mouse cursor freezes for about 20 seconds or so. Then, things go back to normal.

I have the same error reported.

(Late 2007 MacBookPro3,1 upgraded to a 120 GB OWC SSD and 6 GB RAM)

12/10/16 3:56:52.358 PM Safari[375]: tcp_connection_tls_session_error_callback_imp 2110 __tcp_connection_tls_session_callback_write_block_invoke.434 error 22

12/10/16 3:57:08.400 PM Safari[375]: _DPSDiscardEvents: FlushEventsMatchingListFromQueue returned error (-50)

12/10/16 3:57:27.792 PM Spotlight[294]: XPC connection was invalidated

12/10/16 3:57:27.797 PM Spotlight[294]: XPC connection was invalidated

12/10/16 3:57:27.800 PM Spotlight[294]: XPC connection was invalidated

12/10/16 3:57:27.805 PM Spotlight[294]: XPC connection was invalidated

12/10/16 3:57:27.807 PM Spotlight[294]: XPC connection was invalidated

12/10/16 3:57:27.947 PM Spotlight[294]: XPC connection was invalidated

12/10/16 3:57:28.077 PM Spotlight[294]: XPC connection was invalidated

12/10/16 3:57:28.391 PM Console[1237]: Failed to connect (_consoleX) outlet from (NSApplication) to (ConsoleX): missing setter or instance variable

Also experiencing this problem since elCap update. Also having Problems with slow spotlight and incredible slow time machine backup.

Spotlight not working see post by Linc Davis

I have the same issues... iMac 2010 on El Capitan. Spotlight is also slow to respond.

Same problem here. Sometimes it takes up to a minute until Spotlight finally opens, and the console has one entry for every time I tried opening it.