Not a massive user of Connect, but I have persevered to try and use the "Modern" interface, and I am giving up.
I have to say this is probably one of the worst web implementations I have seen in a long long time. It is slow, unintuitive, and generally unresponsive. I often get a blank screen with a few icons, but nothing else. Trying to use the interface when it does load (1 in 5 or 6 attempts) it is just unbelievably slow.
I have switched back to "Classic" permanently (Not temporarily). If garmin force everyone to move to this interface as a permanent feature, then I will be dropping the app and using Stava more instead.