The bug that happened to me is kinda hard to explain since i don’t know exactly why it happened but i’ll try anyways.
We completed the ice fractal as the 3rd and i was jumping around at/on the walls of the bossroom(guess this caused it?) as we got teleportet into the jade maw fractal. As my loading screen finished I saw myself standing inside the jade maw fractal and the next second a new loading screen appeared that brought me back to the, already completed, ice fractal.
I could reunite with my group with the checkpoint at the start of the jade maw fractal (there were still mobs at the big bonfire), but i can imagine it to be quite annoying if you cant manage to die.