In the last beta, (2.9.0.31), the two options of the Split command closes Scrivener. It doesn’t matter if you use it from the Document menu or from the keyboard shortcut (CTRL+K or CTRL+SHIFT+K): it closes anyway.
I use Windows 10 1909 version, 64 bits.
I hope I explained myself well because English is not my first language
I am running Windows 10 and am also not having any crash with Beta 31 when I split windows (vertically or horizontally), nor when I switch back to a single window.