Composite Foreign key to single primary key
The answer is a little bit like the old joke: "Doctor, doctor! It hurts when I do this."

If you want a foreign key to an entity then that entity needs to have a unique key defined to be referenced.

The fact that your Expectations table has a unique candidate key in Expectations.ExpectationId should not prevent you from defining another candidate key that combines ExpectationId and BranchId.  This seems like a violation of third normal form, and technically it is.  However, that is only true because you happen to define ExpectationId as unique.  You could have defined ExpectationId as a sequence within BranchId, such that ExpectationId is not unique on its own.  As it is, you can think of it as the Expectation table defining the combination of two unique values as being the fact of interest.

In any case, if you want to define a foreign key to Expectation that is the combination of ExpectationId and BranchId then there is no way around it but to define the primary key that way.