ABB frequency conversion motor sudden speed reduction issue

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First, describe the fault symptoms: The factory has an ABB variable frequency drive motor, with the drive unit being the ABB ACS1000. This fault has occurred twice; in one instance, the speed dropped unexpectedly, with the rotation speed falling from 160 RPM to 140 RPM. After the operator noticed this, they increased the speed on-site using a variable resistor, and the motor resumed normal operation. The other time was when it dropped from 204 rpm to 0 (the current overload interlock stopped the machine during this speed reduction); the interval between the two incidents was about 2 months. The speed control circuit consists of a variable resistor, a resistance transmitter, an inverter, and a DCS; the DCS merely displays the speed. After the speed reduction fault occurred, no fault code was detected in the frequency converter; ABB technicians also found no error messages. However, during maintenance, it was found that the capacitors on some circuit boards were bulging. I would like to ask fellow sailors if you have encountered similar problems? Please help analyze the cause of the failure. Thank you.