I think I had the same problem, but I managed to find a solution. I had a button group component consisting of 11 variants in which each of the 10 buttons were active (and one with no active buttons). The button I used was a component itself. My problem was, that when I renamed the button labels on my button group instance, sometimes (but not always?!) the labels would change to the labels in my button group component instead of the ones in the instance, when I clicked around in the prototype window - even though it seemed to work, when I cycled through the different variants in the editor. Very weird and quite buggy since I would at least expect to see the same behaviour each time, but sometimes it worked to just restart the prototype, and sometimes it seemed to me, that it would work if I clicked through the different instances slowly before clicking around like crazy, almost like Figma needed time to load all my different instance variants or something like that.
I found out, that I had accidentally changed the labels on the buttons in the button group component instead of just keeping the labels in the original button component. When I reset the text on the buttons in the button group component, everything worked. Hooray! But I still think something is buggy, since it would sometimes work with my original setup and sometimes not - it does not make sense to me, that it does not behave consistently.