Safari slow to load, flooding system.log with launchd errors
I was experiencing the same symptoms: sluggish Safari, with identical errors in the console. I was also experiencing launchd using exorbitantly high cpu capacity.

After much gnashing of teeth, I discovered my problem was a bad spotlight index on an external drive, and after re-indexing the drive, the problem went away. Launchd behaves normally, Safari is responsive.

I do however get the same error in console, although I get it less frequently. It comes in batches of about 20 at once, every 12 hours or so. There seems to be no effect on performance.

Particulars:

'09 MBP 13" running 10.11.6 with the latest public beta security update.

Hope this helps!