It's obviously very annoying when you are trying to make a song and SynthV crashes so I'll be documenting my experience and what's been making my SynthV crash and how to fix it.
SynthV has to render every note and whenever you draw a really long note it has to render that entire thing every single time you change something. So, just place smaller notes, a measure long or so, and it will not only render much faster but also not crash.