Looks like there is a fix in the testing repo:
pve-manager (8.2.6) bookworm; urgency=medium
* fix #5731: vzdump jobs: fix execution of converted jobs
-- Proxmox Support Team <support@proxmox.com> Fri, 20 Sep 2024 17:47:17 +0200
I updated yesterday and also found that my system did not backup last night.
Reviewing what you have posted, I have the same issue and error message in the system log for my backup jobs.
root@pve:~# pveversion
pve-manager/8.2.5/12c0a59769080547 (running kernel: 6.8.12-2-pve)