According to XPHP Variables - LiveWhale Support, you should be able to use <xphp var="details_thumbnails" /> to get the gallery thumbnails on a gallery details page. And in fact that was working as expected on our prod site (LW v.2.16.1). But in testing v.2.18.0 on our dev site, the thumbnails were not appearing. I changed the variable to <xphp var="galleries_thumbnails" /> and it works on prod and dev.
I’m just wondering if this is a bug in 2.18.0 or if the documentation needs to be updated. If it is a bug, I’m wondering if other <xphp var="details_ variables could be affected.