Make sure to respond to the 'Trust this computer?' prompt on your Watch

"invalid mode 'kCFRunLoopCommonModes' provided to CFRunLoopRunSpecific - break on _CFRunLoopError_RunCalledWithInvalidMode to debug. This message will only appear once per execution." still habbening

Deleting the Derived Data folder solved the issue (for now, until it returns and I have to do the same thing over.)