Hi - When using the Dropbox App on my iPhone or iPad, I want to download or save the video. I select 'save video', it starts the download process and when its finished I get the error message "Sorry, this type of video cannot be saved to this device." It is an mp4 video which I used to be able to save with no issues. I can download it using my computer but not using the mobile app. Looking for some help with this please. Thank you!