I had raised this issue numerous times, but very strangely DeoVR never wanted to fix it.
The 3D SBS videos used to be played just fine like SkyboxVR, until one day an update ruined it, and no one in DeoVR bothered to fix it for years.
The logic behind their inaction, just my speculation, is that they don't want users to use their program for 3D movies playback. DeoVR are supposed to play 180 or 360 VR videos only, so even the Half-SBS playback was broken for years, they never fixed it.
So the only fix in DeoVR seems to be converting Half SBS 3D videos into Full SBS 3D video.