Tvheadend

I had similar experience (also ubuntu 16.04 LTS) so I downgraded to ffmpeg to 3.4.4. It would sometimes completely freeze my Rpi2 with Libreelec / Kodi / PVR HTS client that it had to be power cycled.

I removed the ppa and ffmpeg 4.*

sudo apt-get install ppa-purge && sudo ppa-purge ppa:jonathonf/ffmpeg-4

I added the ppa for ffmpeg 3.* and updated the stock ffmpeg

sudo add-apt-repository ppa:jonathonf/ffmpeg-3
sudo apt-get update

After a couple of hours of testing with various stream sources it seems that the stuttering and freezing has gone.

Hope this helps

TVH not use external FFMPEG, there is a build-in one.

Forgot to mention that I'm using ffmpeg pipe muxes hence the external ffmpeg binary version makes the difference in my case.

Yes, that's the point:
with the Automatic IPTV Network type and a M3U playlist containing pre-defined streams, I am using the external ffmpeg version, which doesn't work.
Selecting a normal IPTV network and entering the URL for the stream in the URL box, works without problems.

Njuskalo, yesterday a new version was published by JonathanF.
First tests ran successfully here, could you also test it?

I tested it last night, not a single problem.