Manage captures not showing thumbnails for videos when hovering over them

Open the Upload app, go to My Captures, highlight the video thumbnail, and hit the menu button. Choose Delete.

Or open the Upload app, My Captures, select Manage from the left-hand tab, and select multiple thumbnails at once, and then choose Delete.

YOu don't need to watch them you can just hover over them and wait a few secs and it will generate a thumbnail, This is most likely done by design as it takes CPU and HDD resources to generate them so MS probably did this to save on them until you really
wanted them.

I think the thumbnails should be generated automatically as soon as you go into My Clips. The console is more than powerful enough to quickly generate them without you having to either click on each one or hover over each one.

That is to be expected, once it saves it takes time to process the video. Give it long enough and it would show a thumbnail. Watching the clip speeds up the thumbnail process.

You can go to the video in your recent captures from the mixer section of the guide menu, go to the video thumbnail and press start ( 3 horizontal lines) and upload to the clod by selecting the cloud image. You can try these steps.