Forerunner 745 corrupt activities (.fit files) after 6.20 update

I've had 3 corrupt bike rides this week. I have the forerunner 745 as well (software version 5.90)

You could try to remove old activities and resetting the watch to see if that helps. Failing that contact Garmin support. When I had this issue my watch was replaced under warranty and I’ve not had any issue (so far) with the replacement.

I take running fairly seriously and run around 5 times a week so I decided to jump ship from my FitBit Versa 2 to Garmin, in my case a Forerrunner 245 (non-music) a couple of weeks ago.

I've been loving the watch and the platform so far, it's a completely different experience and has most of what I've been looking for. Surprisingly enough, what I mostly miss about my fitbit was paying directly from the watch, which I used on a daily basis.
Are there any other real upgrades which would justify the €389 price of a 745 vs the €209 of my 245?
The only tangible differences I've found were the music support and the altimeter, which could come in handy as I live in a mostly hilly/mountainous area.
I still have 10 days to return my 245 free of charge in case I decide to.

I have a Forerunner 745 running 6.20 and also getting corrupt activities. The watch is only 1 month old. So far its happened 2 times in the last 5 activities on the eMTB profile while using GPS + GLONASS setting. I also noticed the watch paused itself a few times and on one occasion rebooted during the last activity.

If I explore the activity on my watch I can see all HR data and stats but no map so would appear that the GPS data is missing. In Garmin Connect I have gaps in my HR/Stress/Body Battery data during the time I did my activity. The activity will not sync to Connect and cannot be manually imported into Strava or Connect. 

I had Move IQ enabled which I have now disabled in case its causing a conflict with the activity. I did have my phone with me and Connect was likely running on my phone. My watch was 100% charged and only has a few activities saved on it so has plenty of free space. In addition I was using the power and cadence sensors paired with a Specialized Levo eBike which perhaps contributed to the problem.

Not good and very frustrating! I have posted on this thread requesting assistance to fix my FIT files and/or hopefully get some insight as to what went wrong and how to avoid this happening again in the future before I take the watch back for a refund. forums.garmin.com/.../corrupt-fit-file-repair-requests

Please see response to your other post here - Corrupt FIT File Repair Requests

I've had the same issues you've described in the past. I did a reset and so far no corrupted activities for the last month or so. My theory is that it has to do with turning on the "PULSE OX" feature. It was when I've had this feature ON that I got corrupted activities and random reboots (showing Garmin Logo Freezing). Try doing a reset and disabling this feature as you setup the device.

I have replied with much gratitude in the post above. Thank you again seilogramp! I intend to do some further testing to see if I can definitively re-create the issue while changing variables e.g. remove bike sensors, disable Bluetooth on my phone, try different profiles, etc. and will post my findings here to hopefully help other users identify the root cause of the corruption. In addition if I can find the sequence of events that causes the issue with sufficient evidence I will raise a bug with Garmin to hopefully get it fixed in a future release. And fortunately Garmin has an active community and users like seilogramp who can at least assist us with FIT file repairs. 

I have deliberately not hard reset my watch or deleted all the FIT files from the 'Activity' folder yet so as to try and reproduce the errors that cause a reboot and/or corrupt FIT file and get to a root cause diagnosis.

I did about 20 activities yesterday each about 1 minute long (riding around my driveway and road in front of my house), all on the eMTB profile and (deliberately) did not manually reboot the watch before I started testing. Out of the 20 activities only about 10 were error free so a very poor result of about 50% success rate. I didn't take the time to record each test and write it down so this is a rough estimation of the failures. I realize that this is not very scientific but was all I had the time for so far. 

I did the following tests with no obvious problems:

• Disabling the cadence and power sensors.
• Had my phone on (with Bluetooth enabled and Connect running) and with my phone off.
• Pausing and resuming multiple times as well as cycling through all screens and data fields during the activity.
• Starting the activity with the map screen on and navigating a course. 
• Enabling/disabling Move IQ. 
• Starting an activity without waiting for the GPS to be ready. 
• Pulse Ox set to night time only.

I then noticed that when I was nearby my house and stopped and saved the activity I would get the "Green Triangle of Death" (Garmin Logo) and the watch would reboot, corrupting the activity or losing it completely. I then started and stopped 5x activities in a row in my driveway (close to my Wifi) and got 5x reboots in a row. I then turned off Wifi - > Auto Upload -> Off and started and stopped 5x activities in a row with no errors or reboots. I also reviewed my logs (event and debug attached below for reference) and noticed some Wifi errors, however the errors were not on yesterday's date but perhaps the logs yield other clues to someone who understands them better. 

https://drive.google.com/file/d/1g3rf2Ks-D1vYY4iejSv2MlWWkWmWTdrn/view?usp=sharing 

In addition I had no reboots or corrupt FIT events in my first week of owning the watch. And I did not configure the Wifi on the watch until my second week of ownership. 

My current theories are: 

• There is a bug with the Wifi Auto Upload functionality that is trying to upload the activity over Wifi. The Wifi connection could be unstable because I'm outside my house far from the Wifi Access Point with high latency and/or packet loss or perhaps the watch just doesn't like my current Wifi encryption settings etc. Or perhaps the watch is still trying to finish saving the activity while the Wifi upload is trying to access the activity. I have not experienced any issues with manually syncing over Wifi for normal use and for day to day wearing of my watch in and around my house I have had no Wifi issues. 
• There is a corrupt file in the 'Activity' folder, that previously did not successfully sync, causing the whole sync operation to fail and crash the watch causing the new activity to also get corrupt and the watch to reboot. However if I manually force a sync over Wifi using the watch there is no reboot and it works. 
• The watch perhaps shipped with an older version of the software (I did not check the version when I got it); when I enabled the Wifi on the watch it did an auto-update to 6.20 (I did not check or change the software update settings, but I see that by default auto-update was enabled) which has bugs that break things.  

I will try do more testing and provide feedback if I find more clues. Any other ideas or tests I should try are very welcome. I really love this watch and don't want to return it but the anxiety of corrupt activities each time you head out into the mountains just ruins the experience. 

It’s more than likely a hardware issue. Consider the hundreds of thousands of watches shipped globally by Garmin and the thousands of people running 6.20 (and various other versions) and configurations, not to mention Garmin’s own internal testing procedures. If the corruption was a software issue it would be much more widely spread. My advise would be to contact Garmin support by phone, explain the issue and maybe refer the advisor to this forum article. Insist on a replacement. In my case it was around a week to ship my defective watch back and to receive the replacement which has not exhibited any corrupt activities to date. Good Luck!