Which build of CoreELEC are you using? The current stable build? The 9.2 nightly build? or the new build with Matrix? Each uses a different set of addons.
There were old files after unistalled Tvheadend server addon. I deleted folder and now it works. But I don’t know why ffmpeg addon looks for library in other addon folder and also other addon folder has higher priority. Shouldn’t they be separated?