When making changes to static-host-mapping in Vyos 1.2.6-S1 (with the updated pdns_recursor package) the following error is shown on commit:
[ system static-host-mapping ] sh: /etc/init.d/pdns-recursor: No such file or directory
The router is correctly reporting that /etc/init.d/pdns-recursor doesn't exist - it appears to have been removed when the fix for CVE-2020-10995 was deployed.
It is also found by checking against the router's DNS service using dig that it will return entries from the DNS that were deleted. So it appears that in 1.2.6-S1 the DNS service is not being restarted.
A manual fix for this problem is to issue:
tim@ferrari:~$ restart dns forwarding
Which correctly restarts the DNS service and ensures that the commited configuration is reflected when the router is queried using dig.