Gas Turbine GCV Clamp

I would like to know what you guys think on following scenario:

A Network has 4 Gast Turbines which are synced and all are in Droop mode. One of Gas Turbine among them, has a GCV clamped at 8MW output.
On a particular day, what happens is that even with GCV clamped, the output reduced by 1MW.

What can be the cause of this?

Here are a few ideas:

1- Any of the other Gas Turbine took load and this reduced it's output? But the GCV is clamped so can it reduce its output?

2- The composition of gas has changed so even with the same volume, net output is less? Can temperature play a role here?

3- There is some restriction ahead of the GCV so even with the clamp, flow is restricted and GT output reduced.

Any other cause? What else can be looked at?

What about grid behaviour is there any event that may conduct to this situation...

What is turbine type frame ? Controls systems installed?

I have a MK6e app code showing clamp on GCV for some reason like grid behaviour ..P2 Pressure behaviour...