I did the chasing the sun route again and looked out for when the progress bar disappeared.
It happens when you turn left from Makuri island to Neokyo, it does disappear straight after the turn but a little later, the avatar lurches right and then left momentarily and then the progress bar is gone.
I think this is where the severe gradient change was (which seems to have been fixed now?)
I wonder if the fix for the gradient is to very quickly steer around it but this kicks you off the course you are following?
I experienced this bug today as well. No badge for me! I’m not sure if this is related, but I was also mysteriously given a sprint jersey (I was doing a pretty steady 2.1-2.5w/kg ride, supposedly took the Railway Sprint jersey in 43.28 sec) AND I was almost 31km into the ride when I picked up the jersey, which seems crazy. It disappeared after a few seconds.