Why do I receive the warning "no DMN element referenced in element"?

Hello,

I have a simple DRD and decision table, as shown below.
image

image

and the DRD is just this decision table, as shown below.
image

Why do I receive the warning “no DMN element referenced in element” ?

Thank you in advance.

Please share your DMN file as without it I have to guess what is wrong with the diagram.