Can only retrieve chunks, but status of Udemy support is listed OK

I use Kali Linux rolling release.

When I try to download from Udemy, only small chunks are listed and downloaded. This result as binary data that is not usable at all.

$ dpkg -l | grep -E ‘avc|ffmpeg|downloadhelper.’
ii ffmpeg 7:6.1-3 amd64 Tools for transcoding, streaming and playing of multimedia files
ii gstreamer1.0-libav:amd64 1.22.7-1 amd64 ffmpeg plugin for GStreamer
ii libavc1394-0:amd64 0.5.4-5 amd64 control IEEE 1394 audio/video devices
ii libavcodec-dev:amd64 7:6.1-3 amd64 FFmpeg library with de/encoders for audio/video codecs – development files
ii libavcodec-extra60:amd64 7:6.1-3 amd64 FFmpeg library with additional de/encoders for audio/video codecs
ii net.downloadhelper.coapp 1.6.3 amd64 Video DownloadHelper companion app

Please, advice. I’m an experienced Linux user. Can test alpha releases as well for Udemy and give a hand, if needed.