Composite Model Crashing When Adding an Import Table

Hello, we have a main dataset we use for serving over 100 connected "thin" reports.

The model has been growing fat and slow as any table used for a particular report gets added to it, and stays there forever!

We want this fattening situation to stop and are looking for alternatives (any suggestion?)

One promissing approach, using new composite model + Direct Query over AS funtionality, what we envision is selecting the tables we need from the main data model and then via import add the report-specific tables.

However as you can see in the attached screen it crashes. We dont know what we are doing wrong as this seems like a typical composite model use. Is that so?

Thanks in advance for any help or suggestion, also how to deal with this situation.

Juan