Clip Replace from Source Window Not Working

For years and years, I've used the 'option' modifier key to drag a clip from the source window to a clip in my timeline, and it has replaced that clip. Now it appears not to be working after upgrading to the latest version (23.5). What happens now, every time I try no matter the clip, is the clip in the timeline indicates there's not enough media to replace the clip. I've attached a video of the process.