Can't access or ping IPSec Site-to-Site Local to Remote devices

Hi,

I'm trying to enable an IPSec Site-to-Site connection with a remote location but have a few problems on the route side

Here's my config : 

• Sophos XG - SFOS 19.5.2 MR-2-Build624
• Sophos LAN on 172.16.16.x (set as LAN in Hosts and services)
• LAN port is connected to a router acting for DHCP, DNS and other functions (the router is Synology RT2600ac with VPN Server)
• Local LAN on 192.168.1.x (set as LAN1 in Hosts and services)
• Remote LAN on 192.168.2.x (set as LAN2 in Hosts and services)
• Static route on Sophos for 192.168.1.x to static DHCP IP on the 172.16.16.x range
• Sophos DNS is set to 172.16.16.16
• Public IP address is 10.50.xx.xx

And here's the steps that lead to the problem : 

1. The IPSec Profile is set with the same settings on the Local and Remote servers : 
   
   
   
2. Firewall Rules FROM and TO all three IP ranges (172.16.16.x, 192.168.1.x, 192.168.1.x) :
   
   
   
3. DNAT rules are created as showed here : 
   
4. VPN is allowed to PING and DNS in Device Access
   
5. Site-to-Site connection established and active
   
   
   
6. I can't ping/traceroute Remote devices via Diagnostics / Terminal of Sophos :
   
   or Local device present in the DHCP range of the Synology router : 
   
   
   
7. The ping process works from a Remote to Local server though!
   

I tried a few things I saw on Sophos Community, on Synology's and other forums but can't find a way to make my setup work

Is there anything I could do to make it work?

Thanks in advance and don't hesitate if I can provide anything else

Regards