"The movie files contain no video frames" - cannot important certain mp4 videos

From a about a couple of weeks ago, I can't import most of my mp4 videos. It gives an error message: "The movie files contain no video frames" as in the attached screenshot. The videos can be played by Media Player, so nothing should be wrong with the vidoes. I also tried on some videos I imported before successfully. I saved a copy of them, renamed and imported them again, and now I can't any more! 

What's more weird is that it doesn't happen to all new videos. A few of them can, and it seems to be random. For example I took two consecutitive videos of my phone and tried to import them both. One of them made it but the other one failed. 

To add a detail. All these videos were took with my cell phone. I downloaded them from Google Photos before importing them. Speaking of which, I haven't tried vidoes taking with a digital camera. But I've always been downloading videos from Google Photos and I never had such a problem before. Any idea? 

Thank you very much, 

Wei