Using Classic Outlook on Windows for personal email, calendar, and contact management
Even that it's really annoying and unproductive, don't worry the text will not actually disappear.
The text is only visually disappearing, but will come back when you for example move your window, scrolling in the document, zooming, switch window, selecting all text and etc. The solution seems to differ on different systems.
I've had this BUG for years. Even on different machines. Im stunned that this issue never been solved when so many users globally stumble upon this issue.