I haven't yet ben able to successfully 'reload' any missing media into projects that have missing media. The only situations I've been successful in when media is missing is to use the replace function but replacing with the original piece of media. This has also been the case when a group of say Photoshop files were missing I used the reload function and nothing happened but it I selected replace one would replace and all the others would automatically connect. So why may the reload function not be working?
My understanding is that reload works on a path that already exists- so if you changed something to your source file externally and AE does not automatically update, you hit reload and it updates the file. With missing files the path is broken so reload will not work. Replace does the trick in this situation as you mentioned.