Instruments error: WebKit Threading Violation - initial use of WebKit from a secondary thread

When I run tests against a connected iOS 6 phone, I get the following error in the server log:

[INST STDERR] 2015-04-03 13:45:08.263 instruments[783:46208] WebKit Threading Violation - initial use of WebKit from a secondary thread.

After that, no tests run. I ensured that neither Xcode nor Instruments was running. I get this behavior when running against the node server and against the Appium app (1.3.7). There are a number of other posts on this topic, but they are all closed. One of them purported to offer a solution: be sure “Enable UI Automation” is turned on on the phone. That worked for some people, but not for me.

If "UI Automation " is enabled in your device it should work… I am not able to narrow down the issue… Any other console logs would be helpful to narrow down the issue.

I have a very similar error.

➜  ~ /Applications/Xcode.app/Contents/Developer/usr/bin/instruments -t /Applications/Xcode.app/Contents/Applications/Instruments.app/Contents/PlugIns/AutomationInstrument.xrplugin/Contents/Resources/Automation.tracetemplate -D /tmp/ios/appium-instruments/instrumentscli0.trace -w 39d39a8bf0d6635268e5997dae574c04246f5e2b com.bytearc.SafariLauncher -e UIASCRIPT "/Users/adolfocabrera/Library/Application Support/appium/bootstrap/bootstrap-1f95f319c723b673.js" -e UIARESULTSPATH /tmp/ios/appium-instruments
2016-07-12 14:49:41.348 instruments[5037:1555723] WebKit Threading Violation - initial use of WebKit from a secondary thread.
Instruments Usage Error: Specified target process is invalid: com.bytearc.SafariLauncher
instruments, version 7.3 (60134)
usage: instruments [-t template] [-D document] [-l timeLimit] [-i #] [-w device] [[-p pid] | [application [-e variable value] [argument ...]]]

How can I fix it?