[knot-dns-users] zone event 'flush' on catalog?

Hello! I have here a catalog zone with roughly 230 member zones in it, and I occasionally see the following warning/error in the log: 2023-07-12T18:01:17+0200 warning: [k-catalog.] failed to update zone file (operation not permitted) 2023-07-12T18:01:17+0200 error: [k-catalog.] zone event 'flush' failed (operation not permitted) The catalog itself appears to work correctly; it's transferred to secondary BIND servers and they correctly process member zones. template: - id: default storage: "..." zonefile-load: difference file: "%s" serial-policy: dateserial master: pdns catalog-role: member catalog-zone: k-catalog acl: [ xfr, notify_from_pdns, xfer_to_bind ] - id: catzonetemplate catalog-role: generate acl: xfer_to_bind zone: - domain: k-catalog semantic-checks: off template: catzonetemplate journal-content: none acl: [ xfr, xfer_to_bind ] While pasting the configuration it occurs to me it might be due to there not being a 'backing' file for the catalog. Is that the problem? Is it even possible on a catalog-role:generate to have a file? Thanks for your help. -JP