For some reason, on some sites only, Joomla! forgets to install one of the plugins that come with Akeeba Backup. I have no idea why that happens and it cannot be replicated on any environment under our control. As a result Akeeba Backup's self integrity check kicks in and warns you that your installation is corrupt (because it is). Unfortunately the only thing we can do is disable the self integrity check for the foreseeable future because it's proven impossible to try and fix the Joomla! extensions installer. A new version 4.5.5 without the self integrity check will be published shortly.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!