I have three Cloudron instances, two VPS hosted with Hetzner, one hosted with netcup. I have a Hetzner storage box for backups.
All three VPSs are doing backups on the Hetzner storage box mounted via CIFS (with exact same config, just different backup directories).
On the instance hosted with netcup, backups regularly fail, usually with "code 1 signal null".
Sometimes starting a backup manually works (i.e. the backup complete fine), other times I still get the "code 1 signal null" when running it manually in which case I have to reboot the whole server then I can trigger the backup manually and it works.
After a server reboot, automatic daily backup might work for one day or two and then stops working and fail everyday.
Looking elsewhere on the forum I tried to remount the storage box but it does not help. Backups work fine on the two other VPSs. I also made sure backups don;t happen at the same time on all three instance in case that would create issues.
I have several log files corresponding to each time a backup failed, can you put them up here or is there sensitive info in them?
Given that the backups are working fine on the hetzner instances, this indicates an issue during backup with the mountpoint. Maybe the connection to the storage box sees some hiccups. Those issues are generally quite hard to debug since they are often on the lower system levels Maybe you can also reach out to netcup/hetzner if they see any interruption between their networks during the time your backup failed last time.