I'm pretty sure that plugin won't work with some voicebanks because of the way the oto's configured. Some multipitch voicebanks have suffixes on every pitch, so when it goes to convert notes, it can't find a VCV alias in the oto (ex. らC4 and な; the plugin can't convert the な to "a な" because nothing in the oto starts with C4. It looks for the last character of the alias and will add it to the prefix of the next note, if that makes sense). I think that's the case with Renri's voicebank, and she's not the only one with this kind of configuration.
If that's what's causing the issue, the best solution is to convert the UST with a monopitch VCV voicebank (which will almost always have no suffixes) and then switch back to whichever voicebank you planned to use. Hopefully that'll work? Sorry if I misunderstood the problem ^^;