I can's select some videos from the preview page

Sometimes, when you go to preview the videos that can be fetched, you may see that some of them are stricken through and that you can't select them. Like so:

Those videos have already been added by the plugin on a previous run. They won't be added again, in order to avoid duplicate posts.

That said, you can find the existing posts, trash them, and then go to trash and "delete permanently."

That will allow those videos to be added again.