Automount (with maps stored in FreeIPA) does not work until autofs is restarted

I have a FreeIPA server configured with AutoFS maps (incl. master) and a server sharing /home directories.

I have just installed a new Ubuntu 18.04 server (on a VM) and set it up to automount the /home directories, however the automounts do not work until I have executed 'systemctl restart autofs'.

After booting, autofs logs show:

Jan 10 19:28:37 host-02 systemd[1]: Starting Automounts filesystems on demand...
Jan 10 19:28:37 host-02 automount[892]: lookup_read_map: lookup(sss): getautomntent_r: No such file or directory
Jan 10 19:28:37 host-02 systemd[1]: Started Automounts filesystems on demand.

I've found various references to similar problems with autofs/sssd that seem to relate to old (and supposedly resolved) problems with sssd initialisation not being fully completed before autofs is started, however the old workarounds (e.g. adding an ExecStartPre delay to sssd or autofs) do not seem to help much in this case.

Any guidance on how to go about debugging/resolving this issue would be appreciated.