Sometimes the occ command needs to be run. The occ command is located in /var/www/nextcloud and needs to be run with the www-data user.

_$: cd /var/www/nextcloud
_$: sudo -u www-data php occ db:add-missing-indices
_$: sudo -u www-data php occ db:add-missing-primary-keys
_$: sudo -u www-data php occ db:add-missing-columns
_$: sudo -u www-data php occ db:convert-filecache-bigint