P mag rough after rainy day outside overnight

Had a very rough mag (left - P mag) and no roughness on right (which is Light Speed) during run up this morning.
Went back to ramp and shut it all down. The engine was pretty warmed up by this time.
Started back up and had the same rough on mag check.
Shut it down and waited ten minutes. Started up and RPM drop was minimal as I usually see.
Can the inside of a P mag be subject to 100% humidity effect?
Other than some warming and the shut down process, I can't see why it cleared up.
The P mag has the latest firmware and is just back from a factory check out.
Flew home, all seemed normal. Did several single side tests in flight and saw the normal rise in EGT on all cyls. No roughness.
Any thoughts out there?

Call Emag on the morning but first pull your cowl and make sure all your plug wires are connected properly, both at the plugs and at the P-mags.

(This is where the EICommander can help you identify the issue.)

Agree with Bill. If the P mag failed the engine would have stopped on left. Did you note EGTs, which cylinder (s) went cold? That would tell you where to start looking.

One other thing. We recently had a customer with a cracked clip at the plug. The EIC indicated there was an issue, along with an occasional miss but it took a while for the owner to diagnose it.

When you push the connectors on, wiggle them and see if you hear or feel and scratching.

May be a fouled spark plug ?

thanks!

Thanks for the input. It gives me some data and a starting point to find the root cause. I could not really picture moisture getting ingress into the mag, but it seemed linked to the high amount of moisture. More likely wires or a plug.
Will pull cowl on the weekend and see. Today, I am driving a turbo 210 to Oregon. What a heavy dog compared to an RV......