Your service was redeployed as part of routine infrastructure maintenance. Since your service did not have a volume attached, any data written to the filesystem was stored ephemerally and cannot be recovered. To persist data across redeployments, you'll need to attach a volume to your service.

Where should we add a unit to make it permanent? Could you help us?

You will need to right click your service canvas, add a volume, and select your desired service to mount it to. It’ll then ask for your path, which usually should be set to /data.

In your code, you’ll store files from the /data directory.

I'm in the same situation if a restart or deployment occurs my data is lost, so I had to update to the Pro subscription which you manually or automate backups. Sure enough, yesterday I saw a system redeployment was done and there was an empty database. Fortunately, the restore worked and the database was restored. Just a couple of records I had to recreate of activity in between now and the last backup. But I still need to set up the database for persistence. I've done the /data directory process, but something must be missing. You got to have backup function, unless you don't mind re-entering data which I've always felt is wasted energy.

OP didn't have a volume, so it's impossible to back up the lost data.