some portals result in players screens flashing the correct destination, then teleporting them again to the same location, 1 block down, facing the wrong way.

This happens whether the destination is Worldname w:worldname w:worldname:n/s/e/w, "dest here". This happens whether adjustspawn is on or off. I've checked that the destination for the portals matches the world spawn. /mvtp brings players to the correct location, with the correct facing.

the console gives a "could not pass player move event to multiverse portals" error. Does not give this error when correctly teleporting players.

I'm also having this issue. I'm looking into it now. When I recreate the situation on a clean server environment I am not having the same issue. It is likely that there is a plugin conflict occurring. Will add more as I discover what's going on.