Hi:
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 
With Beta 31, split works fine for me on Windows 7 64-bit. Keyboard shortcuts and menu for split both work fine.
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.
JJE - I don’t think the OP is referring to splitting windows, but to splitting documents (that’s what CTRL-K and CTRL-SHIFT-K do).
Thank you for your comments. I’ve been doing some tests and I’ve been able to narrow down the bug a little bit more.
The bug happens when the split is done on a list item, like in this screen capture.
If you make the split of the document inside any item of the list (e.g, before the “T” en “Test 2”) Scrivener closes (for me).
This has been filed. Thanks.
Apologies! Should read things properly before responding.