Signal problem on some MUXes

  • I was a happy user of Openelec Pi2 with DVB-T once. Unfortunately, a few weeks ago signals from most of my muxes (MUX1, MUX2 and MUX3) began to crash (errors, artifacts, buffering). However the signal from one of the mux MUX8 run like a charm.
    So I have started to try to fix the thing. Firstly I installed new tuner, but it did not help. Then I reinstalled the system to another SD card, then switch the system to Libreelec. Next I tried to put different type of settings in TVheadend backhend and the Kodi. All those actions did not help. I would be grateful if someone give me a clue how to approach this very problem.