Description of my issue:
Hi Nicholas,
I just updated Akeeba Bakup to 3.9.0, then noticed that I get a JDispatcher redeclare error when trying to open the Extensions Manager in the backend. Google led me to the above mentioned thread in your forum, so I disabled system plugins as you suggested and found that the issue comes from PLG_SRP_TITLE which apparently is your own plugin. So I hope you have a fix for it ...
Thanks!