Steam Turbine - "Rotor Stress Evaluator (RSE)" Alarm

We have steam turbine of ANSALDO (Italy) coupled with 323MW generator.

We have hydraulic governor control system on turbine and control system is DCS (Infi-90/Bailey).

When we synchronize/de-synchronize our machine from grid, sometimes there is an alarm that appears titled as "RSE out for min time not elapsed".

I just want to inquire, what are the possible reasons behind the appearance of this alarm?

I have checked in DCS configuration blocks of RSE (Rotor Stress Evaluator) . . . there is some sort of C Language program behind it which triggers Rotor stress validity flag which I unable to interpret. According to my little understanding, when Rotor stress validity flag gets true, RSE out for min time not elapsed alarm appears.

Can anybody guide me about the possible causes of the alarm? I would be really thankful for this favour.

Regards,
Instrument & Control Engineer