SF flashing error

i also get the same error.My system includes S7-400 and ET200 CPU.In that ET200 there are some analog input modules (6ES7331-7PF11-0AB0), the system works normally.At that time, the production line was shut down for maintenance and an incident occurred that day.The first module has a flashing SF light.Then about 4 hours later, 2 more modules also had the SF flashing error.When testing the signal, interference was detected for a period of 2 hours and then signal loss.When checking the module's channels, the voltage is close to zero in the module's channels.I want to know the possible cause of signal interference and module failure.Thank