Tips and tricks to solve Garmin GPS Watch upload issues (Forerunner 310XT)

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Background:
I use a Garmin Forerunner 310XT GPS watch to track my endurance workouts (running, cycling and walking).  I use it with a heart rate monitor and a footpod. It is a great watch most of the time.  However, once in a blue moon, it has issues.  This article describes some of these issues and how to avoid and/or fix them.
Typical user work-flow for the watch is:
1. Do workout (watch records the workout)
2. Connect watch to computer using a Ant wireless comms dongle
3. Upload the workout to computer.  Depending on the settings it will auto update to the "Garmin Connect" cloud service.

Problem 1: Does not auto-connect to computer
Symptom: Watch refuses to auto-connect When the Ant stick is plugged on to the computer.
Cause: Unknown.
Workaround: Re-pair the watch to the Garmin Ant Agent on the computer.
Probable causes (Anecdotal):
1. A setting on the Garmin watch has been overwritten or corrupted causing the pairing information to not persist.
2. Older Garmin Ant-agent program on the PC is buggy.
Fix that really works: Install the new "Garmin Express" software.  It works like a charm and has a "Sync" button for good measure.
Probable other fixes: Reset the device to factory settings (WARNING: Note that all your workout history will be deleted from the watch if you do this)


Problem 2: Fails upload of workouts after connection
Symptom 1: Fails upload of workouts at various stages for unknown reason
Symptom 2: "Garmin Express" or "Garmin Ant Agent" freezes or terminates abnormally in the middle of uploading 
Cause: Corrupted workout data.
Details: I had this happened to me multiple times after letting the battery run dry during a workout.  Watch complained that the battery was low and then automatically turned itself off.  This seems to corrupt the workout record.  After recharging, subsequent workouts works fine.  However the problem starts when I tried to upload all the workouts.  Uncorrupted workouts starts uploading as normal, however during uploading of the corrupted workouts it fails with the aforementioned symptoms.  Sometimes the "Garmin Ant Agent" attempts a reconnect but this reconnect never succeeds and ends up in a never ending loop. 
Fixes: Figure out which workout is corrupted by viewing each workout on the watch carefully.  Corrupted workouts would have missing laps, GPS or other data.  Manually erase the workout from the watch.  Now you should be able to upload the other workouts as normal.

Problem 3: Uploaded data incorrect
Symptom: Heart-rate or footpod data tapering off 
Cause: Batteries on the Heart-rate monitor or footpod is running low
Fixes: Replace battery on the Heart-rate monitor or footpod

Problem 4: Unnaturally high heart rate shown
Symptom: Heart rate displayed and recorded on the watch is abnormally high.  I have seen 265bpm. 
Cause: Unknown.
Probable causes (Anecdotal and from internet research):
1. Clothing that generates large amount of static such as synthetic clothing
2. Poor connection of the Heart rate monitor electrodes to body
3. Incorrect electrode positioning
4. Low Heart rate monitor battery level
Probable fixes:
1. Isolate heart rate monitor from clothing that generates static.  Another option will be to wear skin tight clothing so as to reduce static generated by flapping cloths.  Although water on clothing has helped some people I did not find this.
2. Get a better heart rate monitor
3. Tighten the heart rate monitor to your body better.
4. Ensure that the electrodes are at their right place (chest bone under your breast, slightly left)
5. Replace heart rate monitor battery
6. Put some water or electrode gel on the electrodes so that they make a good contact with your body.
* I also like the solution by solution-to-heart-rate-dropoutsspikes.html :).  I finally decided to give it a try with a US$15 Polar strap from Amazon. It works like a charm and I get the heart rate I expect from the watch now.

Problem 5: Watch freezes just after starting a workout
Symptom: Watch freezes just after starting a workout 
Cause: Unknown.
Probable causes (Anecdotal): Corrupted previous workout
Probable fixes: Do a soft reset of the watch by holding the "mode and lap" keys


Problem 6: Initial GPS values on workouts are wrong
Symptom: Initial GPS values after starting a workout is non-existent or wrong. 
Cause: GPS fix has not been achieved by the time the workout started
Fixes:  Wait for a proper GPS fix before starting the workout.  It may take up to 3 minutes depending on the weather, cloud conditions, relative elevation of surroundings and overhead cover.

Problem 7: Cannot delete corrupted workout
Symptom: Corrupted workout cannot be deleted even after repeated attempts. 
Probable Cause: Watch firmware is temporary in a confused state
Fixes:  Power down the watch, wait for 20 seconds, then power it back up and try again.

Problem 8: General instability
Symptom: Combination of above problems 2, 5 and 7. Another symptom is more than 1% of workout storage is used even when all the workouts are deleted from the device.  
Probable Cause: Watch data storage is fragmented and/or corrupt.
Fixes:  Do a Master reset of the device using procedure described at Hard Reset
or : (WARNING: This will erase all your watch settings and data)

1. Power Forerunner off
2. Press and hold Enter and Mode buttons
3. Press and release Power button
4. Press and release Lap/Reset (watch will power off)
5. Wait 3 seconds
6. Release Enter and Mode

Conclusion: 
310XT works perfectly most of the time.  When it doesn't these workarounds generally work well.