BN3500 Multiple Channel "Not Ok" alarm

Hi , we had tripping of one of compressor train on BN3500 multiple channels fault.

1). Compressor train tripping logged from BN3500. BN alarm log indicates multiple channels “Not Ok” resulting in tripping. This was self-reset.
2.) During Field inspection Probes were found healthy. Gap Voltage and resistance of the relevant probes were measures and results were normal. Terminations in BN Rack were also inspected and no abnormality has been found.
3.) All the Vibration JBs were inspected and did not find any observation of condensation or moisture inside the JBs. Moreover, NO common JB exist for all these channels whose Fault logged.
4.)Grounding at BN3500 was checked and grounding cable was found connected.
5.)Modules self-tests were performed and all module passed self-test.

after necessary check machine was taken in service and it's normal since last 3-4 days. Questions is what is probable cause for such alarm at multiple channels. Alarm was logged at 06 channels. 04 axial and 02 radial. Also it was logged on 04 cards.