MAN Gas Turbine Acceleration Limitation

recently we have noted a message appeared in Siemens HMI related to MAN turbine says "acceleration limitation" followed by another one "GMV limite stroke." as consequence the hp SPEED limited at about 6100 rpm although the operator was increasing the compressor speed set point in parallel with the load raise.

GT: MAN turbo
duty: compressor drive
GMV range: 0-50 degrees, as found in operation: 22 degrees
GMV: gas metering valve

to note that the anti-surge valve doesn't work well, instability in opening.

I will be so thankful for your replies.

best regards