FYI this also affects ceph bind mounts. (I think it's the same underlying issue so I won't open a separate thread/report.)
Relevant config (readonly mount point):
mp0: /mnt/pve/cephfs-hdd/dump,mp=/cephfs-hdd-backups,backup=0,ro=1
Starting container:
# pct start 105 --debug
run_buffer: 571...