I think mea culpa 
After trying out different things and finally having to reset the router to factory setting after upgrading and then downgrading my conclusion is that it was a misconfiguration of the DNS and/or the address that I was giving to the WireGuard, I have two points in different locations with adjacent subnets and the VPNs are also adjacent but in +10, e.g., 192.168.10.0/24 and 192.168.11.0/24 for the bridge interfaces and 192.168.20.0/24 and 192.168.21.0/24 for the WireGuard interfaces respectively, I got it mixed which is which and I also set up the router in the summer and changed the addresses meanwhile and probably totally forgot to update the configuration on the SFT1200 et voilà .
Now after I checked and double checked, everything seems to be working fine.