bch2_evacuate_bucket(): error flushing btree write buffer erofs_no_writes

On mainline kernel 6.14.5 on NixOS, when shutting down, after systemd reaches target System Shutdown (or Reboot), there is a pause of no more than 5 seconds, after which I get the kernel log line
bcachefs (nvme0n1p6): bch2_evacuate_bucket(): error flushing btree write buffer erofs_no_writes And then the shutdown finishes(?). On next boot, I get the unsuspicious(?):

bcachefs (nvme0n1p6): starting version 1.20: directory_size opts=nopromote_whole_extents
bcachefs (nvme0n1p6): recovering from clean shutdown, journal seq 13468545
bcachefs (nvme0n1p6): accounting_read... done
bcachefs (nvme0n1p6): alloc_read... done
bcachefs (nvme0n1p6): stripes_read... done
bcachefs (nvme0n1p6): snapshots_read... done
bcachefs (nvme0n1p6): going read-write
bcachefs (nvme0n1p6): journal_replay... done
bcachefs (nvme0n1p6): resume_logged_ops... done
bcachefs (nvme0n1p6): delete_dead_inodes... done

I have this happening on every shutdown, and this is my single-device bcachefs-encrypted filesystem root.

Should I try mounting and unmounting this partition from a different system, or what other actions should I take to collect more information?