I developed a watch face, and I've discovered there are several bugs with displaying the cover photo in the Connect IQ Store via web browser. These issues do not appear in the iOS app—but there is no forum for the web browser interface.
First, the cover photo frequently fails to load entirely in the browse listing. For example:
https://apps.garmin.com/en-US/apps/metaCategory/analogWatchFaces?start=30&showAllDevices=false
When it does load, it shows an older photo (not the most recent one uploaded).
I thought maybe this was due to the file being too large. So I tried uploading another file. The interface allows me to upload a new file, and the updated photo appears on the watchface home page (https://apps.garmin.com/en-US/apps/9d25f6ae-a5d1-486c-ad00-9102fd623721), but the updated photo never shows up in the browse listing.