Tons of Apps Uninstalled Themselves and Now I Cant Reinstall Them

[NomadforNature]

I have Nextbook 10 with Android 6.0.1, and yesterday my Facebook, Nook, Pandora, and more apps uninstalled themselves, they are simply gone!
I've tried to reinstall them, but I get the error code 963. I cannot install any of them.
I have unmounted the SD card (physically, because I couldn't find the unmount button anywhere in any of my settings) and I've cleared the cache. I have TONS of space available on internal storage (and SD card) and my WiFi connection is good.
This is frustrating because these are the apps I use most, and the whole point of my having a tablet.

 

[anon(238680)]

See if this helps:

https://www.youtube.com/watch?v=KQcJMIBNwMQ

 

[NomadforNature]

I did what I could, but there were no updates installed on Play Store, and no button to unmount the SD card. What i did, didn't work. Still get 963 error.

 

[NomadforNature]

I also disabled and enabled again the PlayStore App, and I still get the 963 error