Several issues:

1. When VPP is restarted after changes to vpp.py the dependencies are called but static NAT is not configured.

2. From @Viacheslav's tests https://internal.confluence.vyos.com/wiki/spaces/Developers/pages/170000709/NAT+static+v2 (case 2)

We cannot get access to the client-1.
Adding external address to nat addresses resolves this problem

vpp# nat44 add address <external address>

3. Need to add checks for external addresses and ports