"Selected network unavailable" !?

[Tabazan]

Hello,
On my zenfone 6 (dual sim : one US one Swiss), when I'm in Switzerland (using the sim of the main local carrier SIM), I got a message "selected network (pcarrier name) unavailable"
But when I switch on both sims (the american one roaaming in that case) the warning message disappear (but I have the roaming costs of the US Sim.
Can you pleause help ? Thank you. ?

[LP_ASUS]

Perhaps switch the physical position of the SIMs? It might want to default to SIM 1 even though SIM 2 is the network you are located in.