RDS stucked when installing Postgis Extension (2.3.7)

Hey,

I have setup an RDS Aurora cluster with PostgreSQL 9.6.9 (I also tried 9.6.11). I am trying to run "CREATE EXTENSION postgis" on it. But it simply does not do anything (Even after waiting for 20 minutes). Installing other extensions is fine. Is there anything I can do to get it resolved?

Regards,
Thomas