Single Static DHCP Mapping Not Resolving Hostname After Certain Time

[Knogle]

Hey, i hope you are doing fine.

I have most of my services provided by VMs mapped with static IPs accordingly in a Non-DHCP range in OPNsense.
They are associated with their hostname, so as usual, i can access my Proxmox Backup Server by using it's DNS name "pbs" and similar for other services.
There is now this one machine, and i was suspecting the machine, so i set it up from scratch, my Zabbix machine, which is causing issues.
My DHCP/Hostname static mapping in OPNsense works fine for quite a time, i can access my Web-GUI through the zabbix DNS name, but after a certain time, OPNsense won't resolve zabbix as hostname anymore! The other ones like pbs still work like a charm and never caused issues. Only this one.
I tried deleting, re-adding the static entry already, no difference.

It looks like that.
What's wrong here? Even from the OPNsense machine itself, it doesn't seem to recognize any Zabbix host anymore, even though it's still online.
When this occurs, i usually have to reboot the OPNsense machine, and then this specific hostname works for a while again.

I hope someone can help me out on this! Thanks in advance, and best regards!

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