I am not familiar with this model MAN, so I guess I am missing something.
In my case, if turbo slows down and exhaust temps increased, I get a load reduce signal from the safety system. This can be from either (for instance)
1. cylinder #8 high temperature
2. cylinder #8 has a higher mean average temperature compared to the other cylinders.
For me, my power management system then derates that generator in either case. For you it adjusts CPP I assume. But either way, the limitation is caused by one scenario or the other (or something similar), and for me identifiable to a single cylinder, unless it is turbo inlet temp. So if your safety system works similarly, you should know exactly what is causing the load reduction. But of course that is only a start in defining your problem.
Maybe the only real help I can give you is to suggest a users group. There are users groups for almost all MAN models. I got hooked up with the users group for our model by calling MAN Germany, and after only a surprisingly few transfers, I was given the contact of a person in a users group for our model. That is where I believe you will get really specific help.
Being electrical, I start my focus on the sensors, which is why I have been trying to drill down on what specific sensor is initiating the action.