Videos - a ton of them are just black with audio

I don't know what's going on.  Earlier today, I had an issue with an electronic.  The seller asked me to record a video and send it to him.  I did that.  It played just fine on my phone.  Once I downloaded it to my computer, it was just a black window... no video with sound.  I kept on recording the video over and over and they're blank every time.  

So, a few weeks ago, my drives failed in my NAS.  I replaced them.  (They weren't supported drives.  They now are.)  I restored from backup and got everything back.  But, I had to reimport the pictures on the NAS into Synology Photos.  It worked perfect before the crash.  Today is the first day I'm looking at the videos because I'm trying to sort my videos and photos.  The majority of the videos on the NAS are black.   You play it and the video is black but the audio plays.

I can't pin it down to any device.  It happens when the video that synced from the phone on the nas using the nas video player.  I've tried using both my Chromebook and my PC running Windows 10.  The new videos I'm recording are sound only.  I tried downloading the video from Google photos online vs copying it directly from the phone.  Plays perfect on google photos on the web.  It's just a black window when I download and play it.  

Also, a lot of my videos are also displaying a message "Failed to load the video because of a network or server error."

When I download the videos from Google photos to the computer, the nas isn't even involved.

I'm at a loss.  These videos are videos I've had for 15 years.  All of my home videos.  Most of them, I have backups on DVD -R and BD-R so I can always go back to the source to get them back.  Other ones are still in Google Photos and I can use takeout to download those again.  But, it's just weird.  

Situation Info.

Louis

1. Update your video player software: Try updating the video player software you are using on your computer to the latest version, or try using a different video player to see if that resolves the issue.
2. Check video codecs: Make sure you have the latest video codecs installed on your computer. You can download and install the K-Lite Codec Pack, which includes a wide range of video codecs.
3. Check network and server settings: Check your network settings and ensure that your computer has a stable internet connection. Also, check your server settings to make sure that they are properly configured and accessible.
4. Try a different device: Try playing the videos on a different device, such as a different computer or smartphone, to see if the issue is isolated to a specific device.
5. Contact the seller: If the video you recorded for the seller is also playing as a black screen with audio, it's possible that there was an issue with the recording itself. You may need to contact the seller and request a different method of demonstrating the issue with the electronic.