Generally, Garmin Connect freezes when the internet connection is not stable and keeps going away. As, a result- you see an egg-like shell revolving on the screen with no progress in steps.

Connect App Stop Responding due to Loose/ Damaged Device Port
Unfortunately, when everything is working perfect, a loose/ broken pin or damaged cables try to build connection with the Connect app but failed to do so. I found this blog very informative and it increased my understanding about Garmin update to a great extent.