SSH through VPN disconnected on LAN

I’ve the following config: 2 router in cascade, the inner is AR750.
I’ve opened the port forwarding on the external internet router on port 15820 and I’ve opened the SSH on 22 port on the LAN router.
Then, I tested the SSH from the smartphone after having configured Wireguard server on the AR750 and the smartphone as client.
The SSH worked, even directly from within the LAN, with the smartphone, and even from outside the LAN, through the Internet.
In this way I reached the clients inside the LAN.
But then, no more SSH through Wireguard.
Now it works only within the LAN, from the smartphone as client.
Why ?

Can you provide a simple topology diagram to explain your question?