If you define an abstract method in a base class, you have to implement this method in all descending classes. Try the project list, users list, etc.

It goes something like: 
`Fatal error: Class App\Projects\Model\ProjectsModel contains 1 abstract method and must therefore be declared abstract or implement the remaining methods (JTracker\Model\AbstractTrackerListModel::getAjaxListQuery) in JPATH_ROOT/src/App/Projects/Model/ProjectsModel.php on line 22`