Entity model designer missing

I have a subscription, but I cannot find the entity model designer. When I was using a trial, it would pop up when editing a data model. Now it cannot be found.

Have you entered your subscription key in the Subscription Information dialog? It can be opened from main menu -> CUBA -> Subscription Information.

Yes. I have entered it. And the entity model deisgner does show up when I start a new project. But it is no longer working on this older project. How do I get it back?

Maybe the class where you expect entity designer to appear isn’t an entity at all?
Can you present its source code?

Can you try to create new entity in the problematic project and check if designer appears?

Can you present a screenshot of information on the CUBA -> Welcome screen (product versions and subscription) ?