@Marvin_S Thank you for the suggestion. However like I said before the 4G data SIM card did work without any connection problems (or tinkering) earlier this year. A year before that it also worked...

TP-Link M7650(EU)1.1 with latest firmware 1.1.12 Build 240722 Rel.1036n ISP Version: 24071201 Used it feb/march 2024 without any problem on the same 4G network (Qcell).Two weeks ago I started using...