Exact.
Static ones are ok, they are known - and when the lease is renewed, DNS doesn't restart.
Classic DHCP, if checked, will restart DNS.
This is a known subject (I won't call it an issue, but if unbound has a lot of work to do at startup, like rowing through all these pfBlockerNG 's feeds files; and you have a 'light' system (processor, disk, whatever) then yes, it starts to take time).