A few days ago, when I was trying to move my WordPress website to WordPress Multisite Domain System – I accidently lost all my connections between WordPress database and media library. I attempted to move my website using the internal WordPress Importer tool.
Fortunately my website was backed up by UpdraftPlus Backup/Restore, unfortunately the plugin was not able to restore into the multi site system the website which was created in the normal, single WordPress installation.
To get my website restored I had to install a single, exclusive WordPress copy. I did not have to install any plugin or any data apart of just the UpdraftPlus Backup/Restore. Using this plugin and zipped backup files I restored all lost posts, pages, plugin and media library. New database details are not essential – you can use any database name and any username too.
I am afraid that moving a copy of single WP installation to multisite is not straightforward job. It is impossible to do just with any plugin or tool like WordPress importer. It is necessary to have a MySQL and WordPress knowledge about it.
Reasuming – UpdraftPlus Backup/Restore really saved me and let me get my website back! Thank you!