Lost MLAT?

[foxhunter]

Or he is running a Kernel with the known problem regarding CPU usage which is already discussed here.

I would give the solution provided by wiedehopf a try:

FYI New Pi Kernel causes dump1090-fa to run much harder

There is a revertable quite easy way to replace the librtlsdr … It’s been linked in this thread and fixes the issue no matter which kernel you run. Apart from manually reverting, Raspbian increments the library version (and probably fixes the issues in librtlsdr by not using zerocopy), the manual intervention will also no longer be relevant. It uses the osmocom repository or you can just use the precompiled binary from me. Replace librtlsdr on Raspbian · wiedehopf/adsb-wiki Wiki · GitHub