Siemens softstarter turning on and off for no reason

We have an installation with a 315kw motor connected to a hydraulic pump. Motor is controlled with a softstarter, power comes from a genset (700kva). Installation runs fine for couple hours but shuts down randomly. No warnings/errors on the softstarter. When the fault occurs and i turn the softstarter in local mode, it keeps ramping up and down. If we reboot the softstarter the machine is fine again for couple hours until the fault occurs again. Been in touch with siemens for a couple of weeks with no result. Voltage from the genset is stable, verified with power logger. Cabinet is not too hot, has an AC in it. Any suggestions? Softstarter is a 3rw5548.