"Permission Denied" after Purge operation. Various folders now owned by Root.

[Jacksaur]

Describe the bug
After Backrest ran its automated purge operation, my server began failing to backup to the repository anymore. On every run, it eventually fails with

Load(<index/ab4d9df2f9>, 0, 0) returned error, retrying after 552.330144ms: permission denied
Load(<index/1b16fe6d67>, 0, 0) returned error, retrying after 720.254544ms: permission denied

retrying repeatedly, until it gives up. I checked these folders, and both were now owned by Root.
I tried chowning them back to my normal account, "user", but the backup would then fail to actually interact with the repo still, same issue:

Load(<data/805466cd99>, 0, 0) returned error, retrying after 552.330144ms: permission denied

I checked, and that specific folder has reverted to Root as its owner as well.

Some background to my setup, which I expect I have misconfigured and caused all this with: I run the backup on another system, as the Root user, since many of my Docker containers have folders that do not give read permissions to non-root users. The backup is sent to my Backup server over SFTP logged in as "user", the account that has Backrest installed.
I'm expecting that the mixing of backing up files as Root, but saving them to the repo as User are causing the issue? I used to do this with Borg, and it never seemed to have any problems in that respect.

To Reproduce
Steps to reproduce the behavior:

1. Back up files as Root, transfer over SFTP to Backrest repository logged in as another account.
2. Perform purge operation.
3. Future backups will now fail with permission errors.

Expected behavior
Backup succeeds as normal.

Platform Info

• Debian 12
• Backrest 1.8.0