IPSec VPN with 0.0.0.0/0 route and no webtraffic by device

Dear All!

We are using Teltonika for many years.
Since one year, all our Teltonika VPN routers are connected to our Watchguard Firewall with IPSec VPN.
All the traffic is routed threw the VPN tunnel. The VPN is working fine and all traffic by attached clients, is routed threw the VPN. Also DNS lookups from our Teltonika Device is routed threw this VPN. Works as it should!

But what we noticed is, that the Teltonika Routers can’t update the firmware from server and also can’t install or update packages from server.
On Traffic Monitor of our Watchguard, we can see the DNS requests from Teltonika Router, but no traffic after that.

It seems that some traffic by Teltonika Device is not routed threw the VPN.
We also tried setting up “Default Route” in IPSec Tunnel, but this type is not connecting to Watchguard. Only Remote Tunnel “0.0.0.0/0” is working.

Do you have any advice?