Siemens PROFISAFE module problem

[arocon]

We are getting frequent SF light in Siemens PROFISAFE module 4F-DO(P/NO: 6ES7193 -4CG20-0AA0,4F-DO). From this module 3 solenoid valves are connected via another PROFISAFE module 1F-RO ( P/No: 6ES7138-4FR00-0AA0 ).

Could any one please tell me what need to be check ? We replace the module 4F-DO but still the problem is exist. Sometimes it comes frequent and sometimes we do not get any fault.

Thanks