The Missing Entity Filter warning is issued in the following situations:

Check if your process activity has a property set with an Entity Action and set the conditions for which in the listed entity attributes.

The most usual case is to have the process activity handling entity action events for the same entity as the one of the process, i.e., the entity attribute Id of the process activity is set with the entity Id input parameter of the process.

See Also

Designing Processes | About Warning Messages