This is one I've been working around for 10+ years:
one or several off your thumbnails in icon view in a bin either go grey or the media offline orange splash, but when you mouse over them they display the media as usual. Setting a new poster frame does not help. The usual fix is to restart premiere and clear the cache on re-launch, but sometimes I can fix it by closing all the open bins bar the main project one and re-navigating the to the problem bin. It's like premiere loses track of where it is.
This happens most in big projects with lots of bins, and these are also the most annoying to fix, because you have to wait for ppro to rebuild the cache.
Could we not, like in bridge, have the option to clear the cache for that bin, to force premiere to rebuild the poster frame so we dont need to re-start?