If you look around the forum, you will find mine and @JardaB post related to syslog messages.
This “dhcp_host_domain_ng.py” is kind of … @#%@##%@# , i had same issue some time ago (and i had to change that regexp to make it working).
Now it seems to be fixed since 3.10.x TOS (i am not sure how it is in 5.x branche)
it depends if you are having static and/or dynamic domains at use or not (with combination of expand hosts in “dhcp & dns”), if you are using hosts/ethers or not, if you used “luci/hostname” and you have the names there right (it should not start with number or “-” ; and some users noted that “_” in name aslo can cause some issues…, and it did some time ago, now it seems to be fine in my case)
… as i did lot of changes (in dhcp/dns/resolver/domain/hostname) i am not sure what makes it working
Below is what is my setup (i just posted most wanted options …)
my setup
##/etc/config/resolver
config resolver 'common'
option static_domains '0'
option dynamic_domains '1'
config resolver 'kresd'
list hostname_config '/etc/hosts'
##/etc/config/dhcp
config dnsmasq
option authoritative '1'
option nonwildcard '0'
option domain 'mydomain.lan'
option local '/mydomain.lan/'
option boguspriv '1'
option expandhosts '1'
option domainneeded '1'
option rebind_protection '1'
list rebind_domain 'mydomain.lan'
option localise_queries '1'
option localservice '1'
## All my "config domain" are having "lower-case" hostname and without "mydomain.lan" part
## entered via Luci/Hostname web ui
##/etc/hosts
## there i have regular entries in lower case
## manually maintained ....
<IP> <fullname-with-domain> <alias>