When putting a blockquote in a spoiler, the line(s) after the blockquote are not hidden; this does not seem to be the behaviour I would expect? Hovering over the spoiler reveals the hidden text as expected.
>! Line 1 >! <blockquote>Line 2</blockquote> >! Line 3
Line 1Line 2Line 3
I'm using Windows 10 and Firefox 76.