Device unreachable

I have this issue with a Teltonika device running RutOS latest version: device is joined to the network, visible in control panel, but pinging in both directions. (i.e. form another device to RutOs or from RutOS to any other device) fails.
Device is connected to the Internet and fully reachable via OpenVPN.
I cannot understand what’s wrong with It: I did a just plain config

Ok, I did some tests.
Device is a Rutx50, with wan and dual sim.

If I connect the wan cable, it works fine.
If I use the SIM the connection is up (device pings the internet with no loss), zertier-cli sees the peers (4 PLANET and the other 3 LEAFs) but no IP traffic flows in the virtual network between this device and the others in both directions. The other 3 nodes work flawless.

Strange thing is that wan port, mob1s1a1 (first sim) and mob2s2a1 are all under the same rule “WAN” so the same rule should apply to all “external” connection, so I cannot explain why under mobile traffic it does not work. I tried also with a wifi connection uplink and it works fine (and the wifi goes on the same firewall area).

So it seems very much related to the Mobile connection which is from Iliad, but I cannot understand why since the ZeroTier peers are visibile.
It happens sometimes that a couple of pings go through but then all traffic gets down.
Could be fireall at the network operator side blocking Zerotier traffic ?