If you are having problems syncing with Garmin Connect app, one thing you might want to check is how much space you have left on your phone or tablet. If there isn’t enough space to store the activities from your Garmin gadget, your device will not be able to sync with Connect. As for why it's taking so long for your device to sync, there could be several potential reasons. For starters, you might be using an older phone or tablet that doesn't have the processing power to download and store that much data. Your WiFi connection might also be slow, or you might be too far away from the WiFi router. If that’s the case, try moving to a different location with better reception.