Network not cennecting while in roaming

I have a physical SIM and use FP6 with 7.4. This week I was on a day trip in Germany from Switzerland. It was the seconnd time I realized that I have no network connection, just emergency calls. I don’t remember what I did the last time this occured but after some changes of options I managed somehow.

Can anyone suggest me what options I should put to make it work?

I usually use LTE only, automatic connection and the romaing data is allowed.

Please clarify what carrier you are using. Maybe when roaming there is an issue with the APN configuration settings? Does your carrier give any setup guidance / documentation on roaming to other carriers?