Hello! I am using a Raspberry Pi 4 with the TV HAT. I got the channels to work in VLC, however when trying to watch online this is what I get in the logs:

Mar 27 23:29:32 raspberrypi tvheadend[4519]: subscription: 0024: "HTTP" subscribing on channel "Super Polsat", weight: 100, adapter: "Sony CXD2880 #0 : DVB-T #0", network: "DVB-T Network", mux: "618MHz", provider: "Emitel", service: "Super Polsat", profile="webtv-h264-aac-matroska", hostname="192.168.12.51", client="Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/123.0.0.0 Safari/537.36"
Mar 27 23:29:34 raspberrypi tvheadend[4519]: transcode: 0002: 01:HEVC: ==> Using profile webtv-h264
Mar 27 23:29:34 raspberrypi tvheadend[4519]: transcode: 0002: 02:EAC3: ==> Using profile webtv-aac
Mar 27 23:29:34 raspberrypi tvheadend[4519]: transcode: 0002: 03:EAC3: ==> Filtered out
Mar 27 23:29:34 raspberrypi tvheadend[4519]: transcode: 0002: 04:DVBSUB: ==> Filtered out
Mar 27 23:29:34 raspberrypi tvheadend[4519]: transcode: 0002: 06:TEXTSUB: ==> Filtered out
Mar 27 23:29:34 raspberrypi tvheadend[4519]: libav: AVCodecContext: Error setting profile 0.
Mar 27 23:29:34 raspberrypi systemd[1]: tvheadend.service: Main process exited, code=killed, status=11/SEGV

If there are any details I might missed out, please let me know. There is no firewall on the Pi.

Try a different browser and compare the results. Not sure what browser you are using but Chromium Browser seems to yield better results these days.

    While using Chromium-based browsers didn't work for me, Firefox worked but choppy. That is not reception problem, VLC plays fine.

    Ok, I made a workaround: Just connected http://<pi-ip>:9981/playlist to my Jellyfin instance. This allows for the video to be viewed by the browser.