Dear @bitmorse & @gonzalocasas
The problem is finally identified, it was not a software error at all. The power supply delivered with with my iC880a was broken. It seemed to deliver 5v, but only when it was not under load. As soon as a load was put on, the voltage collapsed, and this must have caused problems with the concentrator that are not put in the debug info.
I've tried quickly tried setting it up with another Lorawan service, but will try the TTN asap.
Kind regards,
Sven-Erik Haitjema