Akeeba Backup does not load in the front-end of your site. It wouldn't need to anyway, considering how it is a site backup tool.
Akeeba Backup does come with a framework –a programming library– called FOF. It is the library we use for all of our software. Moreover, some other software uses it too. To the best of our knowledge, the FOF library used in Akeeba Backup 4.0 is backwards compatible to the one used in Akeeba Backup 3.11. It is, however, possible that there is a small incompatibility and a third party plugin (not our code) which uses the FOF library is affected by it. That's the only reasonable explanation. So, try upgrading all of your other extensions?
Nicholas K. Dionysopoulos
Lead Developer and Director
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