It might also have something to do with the .oto and frequency files. UTAU-Synth tends to crash with WIP voice banks. It hates having to render new frequency files for new notes while using old files from previously rendered notes (if that makes sense). For instance, if you've already played the note "a" (so it has a frequency file) and then try to render both "a," "be," and "ju" together, it will crash. You'd have to select and render the other two notes individually before you can play them all together. But don't worry, you'll only have to do this for the first time you use your bank. Once every note has been individually rendered once, you'll never have to deal with it again.
At least, that's how it's worked in my experience. ono;;
At least, that's how it's worked in my experience. ono;;