A family of Microsoft word processing software products for creating web, email, and print documents.
In case you haven't tried this yet:
Click the little arrow in the bottom right corner of the Conversions section of the Equations ribbon, which opens the Equations Options dialog. If the first check box, "Automatically convert expressions to professional format" is not checked, check it.
It's true that clicking Professional in the equation's dropdown menu should do the conversion, but occasionally odd things happen. I also see that automatic conversion doesn't happen if you enter the equation in LaTeX mode. Further, if you then select Unicode mode and click Professional, the results aren't always the same as if it was initially entered in Unicode mode.
My last suggestion would be to try an online repair of Office.