I tried to split out a section from an article by copying and pasting from one Visual Editor tab to another. The text contained one raw reference (which, incidentally, Visual Editor was unable to render in the reference list while editing the new article). When I tried to save the new article or switch it to source editing, I just got 500 errors from the server.
My workaround was to Escape (using the Esc key) from the "crashed" save/switch features and copy-paste the content into a new browser tab, and then to change the content of the reference (which showed up as empty in the dialog box) to "TBC". See https://en.wikipedia.org/w/index.php?title=The_Son_Also_Rises_(book)&oldid=663823722