Running InDesign v19.0, but had exactly the same issue in previous versions -

If I want to swap out an existing font for a new one in a text block in my project, the font does not preview instantaneously or correctly when I am scrolling through the Character menu. Sometimes, the font disappears completely, leaving only black blocks to preview. When I press return the text block does update to the new font but not being able to live preview is making it extremely hard to make design decisions and also see if the chosen font will fit the space assigned in that particular font style. Two examples of my problem below.