In T5144#147124, @indrajitr wrote:

PR for the fix: https://github.com/vyos/vyos-1x/pull/1962

Tested on latest "current" source tree build. Works fine and solves the "old syntax" cache file issue. Thank you for the quick and responsive fix.

@jack9603301 I've tested your updated PR and it seems to work well now. Thank you for the quick response.
@sdev I've tested your PR and it seems to also fix both issues. I did not test anything beyond DNAT port only in both ip and ip6 families.

@jack9603301, your PR solves the NAT66 issue - thank you. However, the change you made to nat.py to try to solve the NAT44 issue is not complete and seem to also require a template change. I'll post additional details in the PR.

Why would you enforce an address? It is perfectly OK to have port-only DNAT66 without any destination address such as:
nft add rule ip6 nat PREROUTING iifname eth1 counter tcp dport 443 dnat to :3000
Problem is that the test logic breaks on this and spits out a wrong statement to NFT that barfs on it.