RDS Postgres Increasing IOPS Never Finishes

I am trying to restore RDS Postgres from a snapshot and then increase its iops. I tried on Friday to restore it and increase the iops, and I let it run for 18 hours, and it never got to a finished state or even into optimizing storage state. I assumed something had gone wrong and I deleted it, and I tried again today. The same mostly happened today, except that this time I got an event that said 'The storage volume underlying the primary host of the RDS Multi-AZ instance experienced a failure.'