I have The same issue with videos from the messenger app and I have uninstalled and reinstalled with no results, my wife has no issue. First time I tried to save the video I was able to watch 5 seconds of it then I forwarded it back to my wife and saved the copy I forwarded and I was able to watch 28 seconds of the 31 second video before I get the cannot play invalid url. And before you try and tell me it's my SD card the files are saved internally