Possible Special Character issue corrupting projects

I'd like to add to this. I'm experiencing the same issue of project corruption, but in my case it's using special characters in any text field (for example in a quiz question). When i copy over some mathematic content from word some characters aren't properly interpreted in Xerte and a unicode unknown character (white square) shows up. When i save and close the project without removing this unknown character, the project becomes corrupt and will show blank screens like OP's screenshots.