Ah yes, looking the end of the filament on the video, it's quite bad. Might get stuck on the heatbreak and MMU is detecting tha it's not feeding and backing it away? This is quite common problem with single nozzle - multi extruder setups, some filaments are worse than others and need some tuning to get working properly. There's different methods to get a better tip, I think that there's a custom version of Prusa Slicer that has more options for this...