Missing Slide Title Characters in Impress

On an apparently random basis (not every title, not every slide, not every presentation), some characters in the slide titles do not show up in impress. They do show up in presentation mode and when converted to pdf, but not when working on the impress document. This is LibreOffice, on an OpenSuse Leap 42.2. Any suggestion on how to fix this? I can provide screenshots.

Thank you!