Hi – did you ever resolve this issue? I’m experiencing the same thing.
I have been working on an edit on 2 different computers (laptop and desktop) with the same external HD and everything has been fine until now, with the edit being identical on both machines.
Now, however, when working on the laptop, as you say, the clip shows up in the browser and the timeline, but when playing the timeline there is the missing clip red rectangle where the clip should be.
I click the missing clip red rectangle and hit ‘reveal in browser’ which then selects the in and outpoints on the clip and perform a replace edit. After this the clip plays back fine but audio and colour adjustments need to be remade. This has also been happening with a ‘missing’ generator. As with the clip, the generator was available in the event browser and showed in the timeline but played back as a missing clip red rectangle.
When I open the library on my desktop however, it all plays back fine with no ‘missing’ clips.
Any ideas?