Mysterious SLAPD.service failure

What type of hardware are you using: Virtual machine
What YunoHost version are you running: 12.0.17
How are you able to access your server: Direct access via physical keyboard/screen
Are you in a special context or did you perform specific tweaking on your YunoHost instance ?: Within proxmox; debian bookwyrm

Describe your issue

I restored from backup (from version 12.0.11). However, it is not starting, as slapd.service does not boost

Share relevant logs or error messages

May 28 22:08:24 yunohost slapd[6473]: @(#) $OpenLDAP: slapd 2.5.13+dfsg-5 (Feb 8 2023 01:56:12) $
Debian OpenLDAP Maintainers pkg-openldap-devel@lists.alioth.debian.org
May 28 22:08:24 yunohost slapd[6473]: ldif_read_file: Permission denied for “/etc/ldap/slapd.d/cn=config.ldif”
May 28 22:08:24 yunohost slapd[6473]: slapd stopped.
May 28 22:08:24 yunohost slapd[6473]: connections_destroy: nothing to destroy.
May 28 22:08:24 yunohost slapd[6468]: Starting OpenLDAP: slapd failed!
May 28 22:08:24 yunohost systemd[1]: slapd.service: Control process exited, code=exited, status=1/FAILURE
░░ Subject: Unit process exited

---- After making that file readable for everyone —

May 28 22:14:38 yunohost slapd[7533]: @(#) $OpenLDAP: slapd 2.5.13+dfsg-5 (Feb 8 2023 01:56:12) $
Debian OpenLDAP Maintainers pkg-openldap-devel@lists.alioth.debian.org
May 28 22:14:38 yunohost slapd[7533]: ldif_read_file: Permission denied for “/etc/ldap/slapd.d/cn=config/cn=module{0}.ldif”
May 28 22:14:38 yunohost slapd[7533]: slapd stopped.
May 28 22:14:38 yunohost slapd[7533]: connections_destroy: nothing to destroy.
May 28 22:14:38 yunohost slapd[7528]: Starting OpenLDAP: slapd failed!
May 28 22:14:38 yunohost systemd[1]: slapd.service: Control process exited, code=exited, status=1/FAILURE
░░ Subject: Unit process exited

Can you share the output of sudo namei -l /etc/ldap/slapd.d/cn=config/cn=module{0}.ldif ?

No, I started with a fresh container (as it is easy to setup anyway).
In my second version, I’ve restored the backup without setting up YUNOhost first (and without deleting some home directories) - which seemed to work; but this also means I cannot share the output of the log anymore…