I have a strange bug that have been there for at least 2 years now and I hope a fix is there in the future :). I have two folders in Plex as typ Movies and the path is like this mounted on a NAS (macOS path)
/Movies/Movies 2K/
/Movies/Movies 3D/
Say I have files like this
/Movies/Movies 2K/Warcraft (2016) - 1080p x264.mkv
/Movies/Movies 3D/Warcraft (2016) - 1080p x264.h-sbs.mkv
If i start play any of them they both come up in Home/Dashboard under Continue Watching with the same length I have been watching on all my devices iPhone, iPad, Apple TV 4.