I can’t get the video to play, but glad to hear closed loop is working well enough. That will certainly be simpler and more reliable anyway.
You’re the third person to try and fail at a pseudo-open loop solution, so I think we’re going to need the dogged determination of a PhD student in a well-equipped lab to ever make it work, or understand why it doesn’t 
I tried it for position control with hall sensors, to do precise positioning between steps after getting as close to the target as the sensors can measure. It always jumped when switching back to closed loop, which often resulted in vibration as it quickly switched back and forth. I didn’t devote much effort to it though, since my motors are geared down a lot so the coarse resolution was fine. And after trying @Nanoparticle’s linear hall technique, there’s no reason to use digital halls anymore aside from convenience if a motor comes with them pre-installed, or the driver (such as B-G431B-ESC1) doesn’t have two analog pins accessible.
@Anthony_Douglas was working on a ventilator fan that needed to be as silent as possible, and open loop gives the cleanest waves. But in his case it also needed to be high efficiency, which meant keeping the current just above stall. He may have ended up settling on flux observer too, I’m not sure.