Tvheadend often buffering and getting artifacts

Hello,
I set up tvheadend some years ago on my raspberry pi2 with libreelec but when im streaming to any device its buffering like every minute. I switched already to a pi 3, to raspbian and i tried different wlan routers but on with every setup its the same problem. I also get many video artifacts. the artifacts are more in hd streams. Can anyone help pls ?