thanks for your reply. I will download the troubleshoot file once it happens again.
The provider could not tell me anything about the IMEI. But just the question. In case the Data SIM is registered with a unique IMEI, I would not expect that it works at all. Which is not the case. As I said it works for some days then it stops.
Can I read out the IMEI of the old D-Link router and set it to the RUT360?