Backup Job no tagging snapshots

Hi there; I am working with AWS Backup in order to protect a few resources I have:
This is my EC2 inventory:
2 VMs with 2 volumes each
1 VM with 1 Volume
1 Volume connected to an AWS File Gateway for a remote volume.

I need to have an specific tag for each volume for internal billing needs; so I created 4 different jobs one for each server.
Job #1 for the Volume connected to the AWS Gateway
Job #2 for the server with a single volume
Job #3 for Server A and its 2 volumes
Job #4 for Server B and its 2 volumes.

I put all settings in the same way, the backup ran perfectly BUT, the snapshots created for Server A and Server B do not have the Tag that the job is supposed to write on them. Tag is simply empty.
The single-volume server and the gateway are OK; they have the Tag that was set up in the backup job..
So, I created a 2 new jobs; deleting job #3, I created job #5 for one of server A's volumes and job #6 for the other; ran again overnight and the snapshots do not have the tags again.

What I am doing wrong? It is quite simple to set up and it works for 2 resources, but not for all of them.

Thanks!