metadata in Nikon video (.mov) files disappears

Usually I am able to add the info I want, such as location, keywords, description, etc.  Occasionaly, I get a message that the file doesn't have xmp and can't hold info.  Stranger is when I have all the metadata entered and saved, but then maybe as in the present case, I went to add something to the headline.  It said it can't hold data, and then all my previous info is wiped out and all the fields are blank. This is CC with .mov files