Hi there
I have wordpress installed in a folder on my domain and the out the box Garmin Connect plugin did not function correctly. Style 1 and Style 2 just did not show anything and Style 3 showed the title and a missing logo.
I tracked this down to the code "get_option('home')" in garmin-connect.php not returning the correct path with the folder name, replacing this with "get_settings('siteurl')" and everything worked.
I did have the widget screen in the appearance section of wordpress administration lock up on me frequently when the garmin plugin was activated and finally got it working by deactivate-ing the plugin deleteing it re-installing it (without activating) editing garmin-connect.php as above then activating and adding it on the widget screen.
Hope this helps
Tim