I've noticed some crazy spikes in resting heart rate (RHR) on the Garmin 235 even when sitting perfectly still at my desk. Here's one example:
Sort of looks like an earthquake (to the right and below the second little workout guy).
This never happens during exercise - only at rest. I filed a formal complaint with Garmin - was asked if I had the latest updates (a 2.5 Elevate module update, and the 3.3 235 firmware - yes and yes).
Turns out they are on the case - working on addressing this with a new upgrade. This is what I heard:
I took a look at your account, and I see the spikes you are talking about. Currently we are aware of some issues with the heart rate on the Forerunner 235, and are working on getting these resolved. This issue will be resolved in a future software update. Although there is no specific time when this update will be out, we are working as fast as we can to get it out to resolve these issues.
So hold on to your hats, the cavalry is coming, eventually.