Unrepairable data corruption on a raidz2 when all drives show zero errors -- HOW???

So just getting around to checking my logs on my backup server, and it says that I have a permanently damaged file that's un-repairable.

How is this even possible on a raidz2 volume where each member shows zero problems and no dead drives? Isn't that whole point of raidz2, so that if one (er, two) drives have a problem the data is recoverable? How can I figure out why this happened and why it was unrecoverable, and most importantly, prevent it in the future?

It's only my backup server and the original file is still A-OK, but I'm really concerned here!

zpool status -v:

3-2-1-backup@BackupServer:~$ sudo zpool status -v
pool: data_pool3
state: ONLINE
status: One or more devices has experienced an error resulting in data
    corruption.  Applications may be affected.
action: Restore the file in question if possible.  Otherwise restore the
    entire pool from backup.
 see: https://openzfs.github.io/openzfs-docs/msg/ZFS-8000-8A
  scan: scrub repaired 0B in 06:59:59 with 1 errors on Sun Nov 12 07:24:00 2023
config:

    NAME                        STATE     READ WRITE CKSUM
    data_pool3                  ONLINE       0     0     0
      raidz2-0                  ONLINE       0     0     0
        wwn-0x5000ccaxxxxxxxx1  ONLINE       0     0     0
        wwn-0x5000ccaxxxxxxxx2  ONLINE       0     0     0
        wwn-0x5000ccaxxxxxxxx3  ONLINE       0     0     0
        wwn-0x5000ccaxxxxxxxx4  ONLINE       0     0     0
        wwn-0x5000ccaxxxxxxxx5  ONLINE       0     0     0
        wwn-0x5000ccaxxxxxxxx6  ONLINE       0     0     0
        wwn-0x5000ccaxxxxxxxx7  ONLINE       0     0     0
        wwn-0x5000ccaxxxxxxxx8  ONLINE       0     0     0

errors: Permanent errors have been detected in the following files:

    data_pool3/(redacted)/(redacted)@backup_script:/Documentaries/(redacted)