Tvheadend

Originally I had a setup with RPi2+USB DVB-S2 tuner running OE5.0.8. After 10-30 minutes operation the Live TV got unstable. Picture freeze, block noise, sound drops etc. Particularly it appears at channel switching. It was completely unusable. I was struggling a lot to locate the fault. I concluded that the problem is reproducible with external Tvheadend backend server hence the problem is located in the HTSP client. I have to emphasize that watching movie from a NAS is stable.
Finally I managed to build a setup which reproduces the fault even after switching on. It contains the RPi2 with and SD card and an USB pendrive with the system. The streaming source is my other HTPC with Tvheadend addon on OE5.0.8. (The same fault comes with a single SD card setup as well, but it needs some hours until occurs)

I attached a complete log from KODI.
At 19:00:08 I select the first channel. It works fine. Then at 19:00:49 another channel was selected. The fault appears immediately. Switching starts with longer black screen, then picture freezes, sound drops and strange buffering information on status display.
See video here: https://youtu.be/LVYc61zk0Gc

In the logs there are many entries about sync and buffering issues.

19:00:57 T:1583313984 DEBUG: CDVDPlayer::CheckContinuity - resync forward :2, prev:4217777.000000, curr:8497777.000000, diff:4240000.000000
19:00:57 T:1583313984 DEBUG: CDVDPlayer::CheckContinuity - resync forward :2, prev:4217777.000000, curr:8517777.000000, diff:4260000.000000
19:00:57 T:1583313984 DEBUG: CDVDPlayer::CheckContinuity - resync forward :2, prev:4217777.000000, curr:8537777.000000, diff:4280000.000000
19:00:57 T:1583313984 DEBUG: CDVDPlayer::CheckContinuity - resync forward :2, prev:4217777.000000, curr:8557777.000000, diff:4300000.000000
19:00:57 T:1583313984 DEBUG: CDVDPlayer::CheckContinuity - resync forward :1, prev:2659422.000000, curr:6787422.000000, diff:2529645.000000
19:00:57 T:1583313984 DEBUG: CDVDPlayer::CheckContinuity - resync forward :1, prev:2659422.000000, curr:6819422.000000, diff:2561645.000000
19:00:57 T:1583313984 DEBUG: CDVDPlayer::CheckContinuity - resync forward :1, prev:2659422.000000, curr:6851422.000000, diff:2593645.000000
19:00:57 T:1583313984 DEBUG: CDVDPlayer::CheckContinuity - resync forward :1, prev:2659422.000000, curr:6883422.000000, diff:2625645.000000
...
19:01:20 T:1583313984 DEBUG: CDVDPlayer::OMXDoProcessing Pause -3.74,-1.44 (A:10 V:10) EOF:0 FULL:0 T:1.60
19:01:20 T:1583313984 DEBUG: OMXClock::OMXSetSpeed(0.00) pause_resume:1
19:01:20 T:1583313984 DEBUG: CDVDPlayer::OMXDoProcessing Resume -3.74,-1.56 (A:10 V:10) EOF:0 FULL:1 T:1.60
19:01:20 T:1583313984 DEBUG: OMXClock::OMXSetSpeed(1.00) pause_resume:1
19:01:20 T:1583313984 DEBUG: CDVDPlayer::OMXDoProcessing Pause -3.75,-1.55 (A:10 V:10) EOF:0 FULL:0 T:3.20
19:01:20 T:1583313984 DEBUG: OMXClock::OMXSetSpeed(0.00) pause_resume:1
19:01:20 T:1583313984 DEBUG: CDVDPlayer::OMXDoProcessing Resume -3.75,-1.55 (A:10 V:10) EOF:0 FULL:1 T:3.20
19:01:20 T:1583313984 DEBUG: OMXClock::OMXSetSpeed(1.00) pause_resume:1

The backend is working fine. The same channel can be streamed without any problem while the problem is present on RPi. I do not understand why the fault comes much faster with USB drive and why it needs longer time with an SD card.
I exclude HW root cause as every part of the system has been replaced individually and had no effect on the fault. The problem is reproducible with FTA channels as well.

Please help me with solving this problem otherwise I cannot use my RPi. It is so annoying.