RUTX50 Whitelist blocks mobile connection

I am setting up a new RUTX50 upgraded to the newest firmware. The router connects well to the mobile network on SIM1 showing connection to the home network. I will also need access of this SIM to operators in a few additional countries, why roaming is not denied. Rather I tried to add a whitelist in operator settings, which also contains the MCC of the country I am in. But after enabling operator settings the router does no longer connect. Even if I add the MNC of the specific operator to the whitelist it does not connect. Is there anything else that needs to be considered to make this work?

So you added specific operators to the whitelist or just whole country?

Just the whole country, this reflects best the tariff structure. But I have also tried to add MCC-MNC for my specific home operator to the list - to no avail.

So now you are in the scope of home network or not?