Unexpected backup failures

[vaschthestampede]

Do you have also another, unrelated datastore which is backed by S3 running on this instance?

No, I do not.

I'm asking since your backtrace includes proxmox-s3-client code paths and there was a recent bugfix for hanging proxy's [1]

I also keep PBS up to date with the no-subscription repository.

proxmox-backup: 4.2.0 (running kernel: 7.0.6-2-pve)
proxmox-backup-server: 4.2.1-1 (running version: 4.2.1)
proxmox-kernel-helper: 9.2.0
proxmox-kernel-7.0: 7.0.6-2
proxmox-kernel-7.0.6-2-pve-signed: 7.0.6-2
proxmox-kernel-7.0.2-6-pve-signed: 7.0.2-6
proxmox-kernel-6.17: 6.17.13-13
proxmox-kernel-6.17.13-13-pve-signed: 6.17.13-13
proxmox-kernel-6.17.2-1-pve-signed: 6.17.2-1
ifupdown2: 3.3.0-1+pmx12
libjs-extjs: 7.0.0-5
proxmox-backup-docs: 4.2.1-1
proxmox-backup-client: 4.2.1-1
proxmox-mail-forward: 1.0.3
proxmox-mini-journalreader: 1.6
proxmox-offline-mirror-helper: 0.7.4
proxmox-widget-toolkit: 5.2.3
pve-xtermjs: 6.0.0-1
smartmontools: 7.5-pve2
zfsutils-linux: 2.4.2-pve1