Sure, I will fill this report with the whole picture. At first the used configuration in both devices / ping test between the endpoints via the outer tunnel IPs first then via the inner IPs.

We do have a procedure to reproduce it.

this is not a support request, we know how to configure tunnels and so on, we're not asking for it.

I'm not sure if you've fully read what I've explained, but this is a regular GRE (IPv4 over IPv6) Tunnel configured in VYOS and in the Huawei Routers. The communication doesn't works in this specific case. If we do VYOS to VYOS then everything is alright. But VYOS to Huawei is not working at all.

In T6108#179246, @Viacheslav wrote:

There is no 1.3.7 version ;)

The issue persists in 1.3.4 too from what I have tested.