Root domain static-host-mapping preventing external subdomain resolution

Not sure if this is a bug or an issue with my setup, I’m not at all confident with my understanding of networking concepts.

We run a variety of subdomains, some are hosted remotely, some are hosted internally, for example: - internal - internal - external - external

When I put in a static host mapping to resolve the internal root domain to a local ip address, neither Vyos nor the downstream clients are then able to resolve external addresses and NSLookup reports ‘non-existent domain’.

Vyos (1.4-rolling-202107010537) is set up as DNS forwarder using servers and