Mobile Data Switching not working anymore on iPhone 11 Pro

Hello,

I am having problem with the connection on my iPhone. I have an eSim and a normal Sim on my phone, i.e. two data plans. I am using the eSim as Default.

When calling or receiving a call from my normal Sim, which is not the default line, I cannot access 3G or 4G and go online. I have the function 'Allow Mobile Data Switching' turned on, Data Roaming turned on, and I tried resetting Network Settings twice. Also, I tried a hard reset, taking the normal Sim out, deleting the data plan and creating it again. It still does not work.

If selecting the normal Sim as default data line, it works, so I assume it has to do with the settings somewhere. Especially since it did work some months ago, but suddenly it doesn't anymore. Anyone know what to do here? It is quite frustrating..

Thank you!