Playback error - transcoding settings

[catakdd]

Hello,

I have a jellyfin setup on my own home-server and I think that I messed up some transcoding settings.
My mini server has the following specs:
i5 6400
8GB RAM
no GPU
I'm using docker on a separate user if that's relevant at all.

I have this issue on some of the movies in my library: "Playback failed due to a fatal player error"
Log: https://pastebin.com/XSWpQPvk

I think I messed up the settings when playing with the transcoding options. I had some issues where my CPU was at 100% used by ffmpeg while playing a movie so I thought I need to change some settings. Looked up what is available for i5 6400 and ended up checking:
Intel QuickSync (QSV) 
HEVC, MPEG2, VC1, VP8
Prefer OS native DXVA or VA-API hardware decoders
Enable hardware encoding
Enable Intel Low-Power H.264 hardware encoder
Enable Intel Low-Power HEVC hardware encoder
Allow encoding in HEVC format
* All the other options are disabled (default)

Can someone help me or guide me where to find additional information about the encoding settings? I'm new to this and I have no ideea whats good and whats not right for my CPU.

Thank you!