Sorry, what's the issue here?

the volume seems to be not mounting - no data but the size of the volume is almost 1gb

When did you observe this issue to have started occuring?

After we detached volume from pg-service and attached to pgvector-service.

On staging it worked perfectly, volume was moved to new servcie.

But on production, the data haven't appeared on pg-vector service.

We restored from backup the data and attached to pg-service, but the data is empty, volume is 1GB size.
We sshed to mounted folder and mounted folder has 42mb size.

You mentioned that this showed when you unmount. PG creates a new DB on the folder that is mounted to the new instance, just because it's PG doesn't mean that the data nor the volume is compatible.

You will need to reattach to the old mount point on the old DB to see your data.

We have reattached to the old mount point on the old DB and dont see the data.

Then I wouldn't know when/where your data is. According to the vol. the 1 GB of data is indeed there. You will need to see where it's at for PG to recognize the data.

Same migration process went flawless on stage envs (exact same setup) but corrupted on production, please ask your devops/admins to reveal where the data is, issue is on the railway side.

That's not the error that seems to be in place. With that said, Railway's databases aren't managed, so if the DB wasn't gracefully shutdown then unfortunately that is an issue that needs to be resolved by you and your team.