Ah yeah it does make sense that the desync mitigation system would stop the tempo sync from happening. Next update will remove the that, so it might work there. Although since it's also removing the framerate cap, it won't matter. Although unfortunately vsync cannot be turned off on browsers (not in chrome at least, there is technically a way to force it off using arguments on its shortcut, but that seems to break other stuff, the maps just don't play correctly at all for some reason despite them playing fine at unlocked framerates in the windows version?), so it'll be only for the downloadable build.
I get around 1800-2000fps when playing the downloadable version (with a 5600x and 4070), which equates to a frametime of about half a ms, so enough to fix it for me at least lol.