Problem with resolving names for internal hosts

[MarekWojtaszek]

In my home network I have an internal DNS server hosted by Synology DSM. The latter is serving my internal DNS hosts names and is forwarding DNS queries for external hosts to Google DNS service. Simple and straightforward setup.

My DNS server IP was added to the System > Settings > General, DNS servers field in OPNsense, as well as the DHCP configuration for the LAN interface.

Everything is working great for all my devices, i.e. both internal and external host names are being resolved correctly. If the internal network names have their external equivalents (for example my www.wojtaszek.it) the name is being resolved to local IP (192.168...)

For some reason though the OPNsense server itself can't resolve my internal host names i.e. when pinging www.wojtaszek.it I am getting the public IP address (91.90.179.152), not the private one (192.168.... etc).

It worked fine for me before and at some point stopped. What do I do wrong? How can I troubleshoot that?

[MarekWojtaszek]

I am sorry but just after posting the above question I enabled the following option:
Do not use the local DNS service as a nameserver for this system
and since then I was immediately able to ping the internal hosts from my OPNsense firewall!

Hopefully I did not break something else with it

Marek