Update: I was looking through my files on TrainingPeaks. On the same sections where Strava wasn't recording my metrics, it wasn't appearing in the graph below the map on TrainingPeaks. This leads me to believe that this is a Garmin issue and not a Strava issue. I contacted Garmin this morning. I am sending back the Edge 840 and will be getting an Edge 540. I previously had three Garmins in the 500 series, and never had an issue in or after the rain. I've read that others have had similar issues after riding in the rain with Edge 840s. Thanks for the suggestion to contact Garmin's customer service!