I got closer to a working setup by increasing tx gain and the scanner sometimes decodes RSRP, RSRP and CINR but it also appears to loose synch to the cell. Over a period of 30 seconds I get quite good measurements part of the time, bad measurements part of the time and no measurements at all part of the time. Over the course of one hour it was only able to succesfully receive and decode one MIB. A UE can sometimes detect the NW, but without a proper SIM it cannot of course register on the found NW/cell. The scanner has no problems with the live commercial networks and their cells.
The PC has p_states, c_states, hyperthreading, etc disabled and CPU clock is stable. Running a low-latency kernel on a quite capable CPU. I don’t get any “L” printed in the console