Since this happens every month after your site is down for a while I believe it has something to do with your host, namely that they are restoring a backup of their server or at least the database every now and then. Besides trying to install Akeeba Backup on your site again, without uninstalling it, I don't think there's anything else you can do about it on your end :/
Nicholas K. Dionysopoulos
Lead Developer and Director
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