MultiXact member wraparound protections are disabled

Hi,

We run postgres 9.4.5.

Starting this morning, we started seeing messages like the below:
Oct 12 14:07:15 site-db01a postgres[11253]: [106430-1] app=,user=,db=,ip=LOG: MultiXact member wraparound protections are disabled because oldest checkpointed MultiXact 1 does not exist on disk
Oct 12 14:09:26 site-db01a postgres[11253]: [106526-1] app=,user=,db=,ip=LOG: MultiXact member wraparound protections are disabled because oldest checkpointed MultiXact 1 does not exist on disk
Oct 12 14:14:18 site-db01a postgres[11253]: [106608-1] app=,user=,db=,ip=LOG: MultiXact member wraparound protections are disabled because oldest checkpointed MultiXact 1 does not exist on disk

Our autovacuum_freeze_max_age = 1750000000.

site=# SELECT datname, age(datfrozenxid) FROM pg_database;
datname | age
-----------+------------
site | 1645328344
template0 | 1274558807
bench | 1274558807
postgres | 1324283514
template1 | 1274558807

So we’re about 100 mil transactions away before we start vacuuming to prevent wraparound.

We’re running precautionary vacuums on our largest offenders to try and drop our transaction ids

What I’d request some clarity on is the message above. What does it mean that "oldest checkpointed MultiXact does not exist on disk”? Would we lose data if we did have to wrap around?

Is this telling us we’re not vacuuming effectively enough?

Thanks,
Karthik