I have the problem, that if had started Engine DJ one time on my Mac and I close it, and afterwards I start Lexicon I recieve the error in Lexicon Sync " “Please exit Engine DJ to continue”.
When I restart my mac run Lexion directly everything is ok.
You can run the beta version of Lexicon (you can change in the bottom of the settings) or make sure no process with Engine DJ.app is running. In this case there will be a crashpad handler process running. You can kill it with Activity Monitor.
Using the beta is easiest.