Postgres 9.4.9 has a fix in it's release notes which reads (emphasis mine):
Prevent possible failure when vacuuming multixact IDs in an installation that has been pg_upgrade'd from pre-9.3 (Andrew Gierth, Álvaro Herrera)
The usual symptom of this bug is errors like "MultiXactId NNN has not been created yet -- apparent wraparound".
I am currently chasing errors in PG 9.4.5 which read:
2019-10-19 15:37:17 EDT : [1-1] ERROR: MultiXactId 1074790449 does no longer exist -- apparent wraparound
Does the above fix in PG 9.4.9 address the error I am getting?