Anything is possible, but Yamaha does not think there is a problem
And after thinking about it, there are two, maybe three reported cases from PSR Tutorial, of the SX900 freezing at the logo screen. So perhaps it's not really an issue at all.

It sounds more like a few isolated instances. If this was a real problem, with numerous complaints, I would think Yamaha would want to quickly find a software fix, rather than have to deal with returns and replacements.