If you have issues seeing some or all of the photos that were uploaded in one of your groups' albums (for instance, a loading wheel keeps spinning on them, but they never load, or they appear as blank), there's a high chance that those images have been uploaded in HECV format — most probably through an Android device. As this format is currently not supported, this could create some issues when you try to view those images.
A useful workaround for this is to re-upload the photo(s) by converting them to JPEG before uploading them.