My Fenix 6X Saphire just got bricked by 16.70. I had restarted it a couple times since the update, because I was still having the same battery drain since 15.20. 2 nights ago, it powered down because the battery was dead. I charged it overnight and went to turn it on yesterday, and it was stuck in a boot loop. None of the hard reset tricks worked.
Called Garmin and 5 minutes later they were sending me a new one. No charge even though it's out of warranty. They said it was free because the software update did it.
I checked this page for Garmin's latest updates for the watch, and noticed that 16.70 was gone and they are showing 15.20 as the newest version.
https://www8.garmin.com/support/download_details.jsp?id=15031