I tried to change the paragraph style for the default Title style. But I have to change the style to in a text box to another style and then back again before it works. See video
It sure looks like a bug of some kind, but I’m sure the team is going to want to see the file to confirm. You can post it here or send it to them via email.
This works as expected for me. I guess you have already applied some kind of override to the text in the frame before you changed the font. If you’ve already explicitly set the font on some selected text, then changes to the paragraph style won’t automatically apply.