I found the issue for the Marbles switch positions not being transferred properly when going from VCV to MM. See here: Marbles - Clock Range and Pitch Range is not passed to MM - #2 by danngreen
But I don’t know what you mean about Muxslicer… I tried a patch feeding in an external clock and it ran at the same tempo on MM and on VCV. Can you be more specific or provide a VCV patch file so I can test it?