Does the Postgres 9.4.9 update fix MultiXactId "does no longer exist" in addition to "has not been created yet" errors?
I upgraded to PG 9.6.8. This particular environment is a legacy application that runs on an "appliance" style deployment so I'm forced into only updating to certain versions. 9.6.8 was the smallest increment I could take.

The initially appeared to have solved the MultiXactId xxxx does no longer exist problem with some simple queries. Subsequent queries to create indexes failed with the original error.