MP4 video layer not visible

I've just loaded up a project I'd previously been working on in a previous version of AE Beta, and bizarrely, two of my video layers are being treated as audio files:

There is no eyeball to switch on the layer's visibility.

If I open the layer to view it, there is no video to view. But if I open the source file in the Project (in AE) it plays back perfectly. If I drag the footage to the New Comp icon, the new comp opens as usual, and the footage is in the comp, but it's the same story - no eyeball to switch on. I shall transcode the file to something else and see if that helps. Yes, it did - I converted it to a ProRes422, replaced it and it now works. Odd.