Yes, Berts remarks made me decide to shut down everything.
I occasionally got bad (better description = unrecognized) packets, but never as much as the last few days:
I can't make much cheese of that, however, stupid of me: those 30xxFx packets point to the RFXMeter packets. So i should have started taking out batteries in the area close to the RFXMeter, i didn't, so that is why i found the bad MS13 at the end...lesson for the next time.
The single misbehaving MS13 was interfering with everything else, that's how it was. It looks like it was constantly sending out garbage, interfering with all the rest. Now that i had all batteries out, i've replaced them all with new ones. The bad MS13 is doing ok again