4K Video Downloader just parses all possible formats and resolutions, provided by YouTube and downloads them. Unfortunately, YouTube has changed the way 360 degree videos are stored.
720p MP4 is the only old format, that can be opened with desktop media players, such as GoPro. http://www.kolor.com/kolor-eyes/
All the other resolutions, which contain 360° after parsing are of the new format, which can be played with VR gadgets.
We would be grateful, if you could share with us desktop media players, that can open such videos.
The problem is with 180-degree VR (VR180) videos, not 360. The new format (equi-angular cubemap/EAC) 360 videos are a separate problem and can be played correctly with certain VR players like you said. They can also be downloaded in the normal format (equirectangular) with some other apps like ClipGrab or youtube-dl.
Here's an example of what a VR180 video should look like when downloaded and played in non-VR mode: https://imgur.com/a/a67y7sb
This is what that same video looks like if you download it now: https://imgur.com/a/HeAti5z
Link to the video on YouTube: https://www.youtube.com/watch?v=drU_nGELMjc
Sometimes when the video is still processing, it's displayed as side-by-side (SBS) on YouTube, and if you download it during this time it will also download as SBS. That's how I managed to download the 3D/SBS version of that video.
That post is about 2D/3D 360° videos downloading in EAC format instead of the standard equirectangular format. We're talking about 3D 180° videos downloading as 2D. They're totally different issues.
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VR180 3D YouTube videos - only video for left eye is downloaded