At least since 02/11/2021, the messages below appear in the log:
admin@ro-lab-01:~$ sh log dhcp | match denied Feb 22 21:28:13 ro-lab-01 dhcpd[3361]: Can't create new lease file: Permission denied Feb 23 06:15:07 ro-lab-01 dhcpd[3361]: Can't create new lease file: Permission denied
Here are the details about /config:
admin@ro-lab-01:~$ ls -al /config/ total 56 drwxrwxr-x 7 root vyattacfg 4096 Feb 22 20:05 . drwxr-xr-x 1 root root 4096 Feb 22 20:03 .. drwxrwsr-x 2 root vyattacfg 4096 Feb 22 20:05 archive drwxrwsr-x 2 root vyattacfg 4096 Feb 16 15:28 auth -rwxrwxr-x 1 root vyattacfg 13022 Feb 22 15:45 config.boot -rw-r--r-- 1 dhcpd nogroup 2274 Feb 23 07:02 dhcpd.leases -rw-rw-r-- 1 dhcpd nogroup 1932 Feb 22 20:05 dhcpd.leases~ drwxrwsr-x 2 root vyattacfg 4096 Feb 22 15:37 scripts drwxrwsr-x 2 root vyattacfg 4096 Feb 16 15:28 support drwxrwsr-x 2 root vyattacfg 4096 Feb 16 15:28 user-data -rwxrwxr-x 1 root vyattacfg 0 Feb 16 19:24 .vyatta_config -rwxrwxr-x 1 root vyattacfg 36 Feb 22 20:03 vyos-migrate.log