I don't have a simple reproduction as our codebase is stuck with graphql-core 2.x (which is a legacy branch), but we often see the garbage collector report reference cycles created by orphaned Promise objects that reference a stack trace that in turn points back to a local scope that contains the Promise.

Adding a simple destructor gets rid of this problem and allows objects to be freed without relying on the garbage collection cycles:

class Promise:
    ...

    def __del__(self) -> None:
        self._fulfillment_handler0 = None
        self._rejection_handler0 = None
        self._promise0 = None
        self._traceback = None