Chris,
The warning is caused by this step in the java action that is called after startup:
Core.addUserAction(IPRangeCheckerLoginAction.class);
Seems to me that the warning shown is incorrect as the user action is being added in this step. As the function works I would not worry about this. This is not caused by your upgrade as the warning is also shown in lower Mx versions.
Maybe someone from Mendix could enlighten us on the cause of this warning and indicate if the method is used incorrectly or a bug is present.