"Unexpected Error" randomly showing up while pitchbending

Monochrome Rose

Teto's Territory
I rarely tune, but this time I tried to do all the work myself. Problem? Whenever I make a control point for a pitchbend, there's a slight chance that UTAU will randomly show me an "unexpected error" popup that won't go away no matter how many time I click any button available. I can't save my progress or even exit UTAU without killing its process in Task Manager. It already happened to me three times in 2 different USTs. What should I do and what is actually written in that small window?
I tried to google the issue and saw nothing similar to my case. A screenshot of the error is attached below.

screenshot.png
 

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