High Pressure Compressor Tripping on Surge during Start up

Compressor Details:
Gas compressor, Dresser Rand, Siemens PLC, Two Custom Controls Anti Surge Controllers (One for each stage), Two Stages, Centrifugal Compressor, Inlet Pressure ~5 Kgf/Cm2, Discharge Pressure on full load ~66-70 Kgf/Cm2...

While trying to load the machine, the compressor repeatedly goes into surge, (-ve deviation is observed in first stage ASCV) as a result, the compressor repeatedly trips on Suction Pressure High...!!

Why is it necessary to have a suction pressure high trip associated with compressor...?? How does High Suction Pressure Trip safeguards the compressor...?? What can possibly go wrong if Suction Pressure occasionally goes high...??

Is it possible for Surge Line of a Compressor to change over time (the compressor was commissioned about 5 years ago)...??

Thanks in advance and regards