Unable to see Strava Flyby for an activity?
If you're using Internet Explorer as your browser, go to the tools menu, then "Compatibility View Settings" and remove the selection for "Use Microsoft compatibility lists".
Check your privacy settings to make sure that "Everybody" is selected for your Flyby preferences. If you select "Nobody" then the Flyby feature will not work for you.
Lastly, make sure your browser is updated to the latest version or try another browser. There may be issues with older versions of Safari, version 10 and lower.