Weird Backup behaviours with Docker

Weird one, which I have no explanation for.

I have Docker running on and LXC (I know, don't say it) which hosts a few Arr services.

Proxmox backs up to a PBS on another server.

Last night, my backup ran as normal and when I got up, 3 of the arrs we're just gone. Restored easily enough through docker compose, but seemed like a really weird thing to happen.

Anyone seen something similar in their setup?