iMovie - exported video freezes at the end!

Okay, so I'm having this weird issue. It seems to have started out of nowhere (not following an update or something I'm doing differently). When I view my movie in the editor, everything looks fine. However, when I export it, it always freezes for the last few seconds.

I end the video with a fade to black transition, and that has never been a problem until recently. Now it freezes just before the fade would normally happen - the audio continues, but any visuals freeze. I tried using a cross dissolve to a black image, which looks the same as a fade, but that freezes as well.

Any idea what could be causing this and how to fix it? It's driving me crazy and it's making me unable to create my videos. Any help would be much appreciated!