After doing an update to 4.7, all widgets are missing. I queried the database for any records wp_options like '%widgets%' and all is the same as the backup. What can cause this or how can the widgets be restored?
I had to restore sidear_widgets in wp_options and any other entries with option_name including 'widget' from a database backup to resolve. Something must have go wrong during the update and all widget settings were lost.
Your update probably went wrong.
Start again from the update page, or upload the missing/incomplete files by ftp.
If you want to verify manually, you will find the related files in
widgets.php and widgets folder with classes for core widgets.
Hope it works after.
Next step would be to look at your PHP error log and see if there are any clues in there. You may have an incompatibility issue. Make sure all plugins are up to date as well.