Since the ‘Media Uploads’ folder doesn’t exist, I wonder whether you have been able to successfully upload from your device to the server?
If you have, then it may be in a location specified on the server page > Settings > Server > Manage > Libraries > Photos > Mobile Photos > (Edit) > and check ‘Add Folders’ - is a different location specified there?
If a previous setting has been changed/lost, you may also search your entire disk for ‘Media Uploads’ to see if it’s found somewhere. Another search option, if you’re still able to upload pictures: do it again and try to locate the pictures on your drive.