Trouble importing videos to iMovie from Canon Vixia HF R600
If you open finder, look in the storage card instead of using imovie. Sometimes the camera makers store files in other directories than the one indicated for current images 

If you can find the files, drag them to a desktop folder and try importing them from your folder instead of directly from the card. Once things are all saved, using the camera or the Mac to reformat the media usually clears up the multiple folder confusion.