The latest Android Garmin Connect update (4.2) rendered my Watch (Forerunner 735XT)/Phone (Xperia X Compact, Android 7.1.1) useless! Continuous sync failures, I was even not able to do settings like Watch face, etc. Neither Smart Notifications worked!!!
Garmin made a huge mistake by releasing this update 5 days ago. I deleted this app, and went back to the previous version one step, 4.1.11 (get the apk from a reliable source!). EVERYTHING works fine again! So if you have such issue: complain to Garmin (I will do!), and revert back to an older Garmin Connect version...