Well after a full night seems I have figured it out.
Even though the veeam intergration services upgraded ok, and I had rebooted each node. I finialy uninstalled all the veeam services on each node and thenthe cluster in veeam. Had veeam rediscover the cluster and reinstall all the services. After that the backups are now working.
Point of interest. One if the vms I backed up had snapshots,after the backup completed it automatically started merging the snapshots!! I don't have a problem with this but just a heads up.