The gallery thumbnails are not appearing because the Facebook CDN no longer permits hotlinking (i.e. accessing and using images and other assets directly on pages on domains for which the content is not intended). The plugin will need to be updated to pull down all those images and upload them to your personal sites before it will ever be useful again. Your best option now would be to download the images yourselves, upload them to your sites, and create galleries manually or with another plugin.
I am having the same issue and have some extra bit that might aid in tracking down the issue. In admin/admin_menu.php, line 151, I printed out the result of the attempt to retrieve the list of chapters:
Array
(
[0] => stdClass Object
(
[result] => error
[messages] => Array
(
[0] => Please upgrade to Salsa Enterprise to use the Salsa API.
)
)
)
I contacted Salsa support, and they told me that all accounts have API support.
