I’m going to start with some caveats that the ability system is not ready for general use yet. It is being used internally but is still being actively worked on. Use at your own risk. If you do use it features that you’re depending on may change or disappear without warning. I wouldn’t recommend using this system yet unless you know you need it and have experienced programmers on your team.
That warning means that you have an ability that should be started by your local client but someone else (either the server or another client) is trying to initiate it. Since you said that it works fine when the net execution policy is ServerInitiated you’re probably trying to activate the ability on the server. Check your code that activates the ability and verify that is only being run on the local client and never gets run by the server.