Sounds like wet electrics, possible a connector.

Are there any codes stored in the computer? Dealer or independent with OBDII (I think) scanner can check to see if the computer can tell you what went wrong.

Did you notice any significant corrosion on the resonance flap actuator that might get more 'sticky' when exposted to wet/dampness?

If you are brave, you could try misting various electrical connectors with water, then go for a drive while they're wet to see if it duplicates the problem. Intermittents, as you probably know, are darned difficult to diagnose, and impossible unless the computer remembers or the fault re-occurs.

Best regards,
Jim