I tried deactivating all the plugins relating to pictures or video etc to no effect.
The theme is Weaver II and for all posts, which includes your galleries, there are these option boxes. Maybe they indicate something that needs to be ticked:
“Per Post Options
These settings let you control display of this individual post. Many of these options override global options set on the Weaver II admin tabs.
Display as full post where normally excerpted.
Display post as excerpt
Show Featured Image with post
Show author avatar with post
Mark as a favorite post (adds star to title)
Hide Post Format label
Hide post title
Show link to single page icon at bottom of post
Hide top post info line
Hide bottom post info line
Hide the comment bubble
Hide Sidebars when this post displayed on Single Post page.
For Masonry multi-columns: make this post span two columns. (●Pro only)
Disable Visual Editor for this page. Useful if you enter simple HTML or other code.
Allow Raw HTML and scripts. Disables auto paragraph, texturize, and other processing.
The above settings are not used by the [weaver_show_posts] shortcode.
Per Post StyleClick for help
Enter optional per post CSS style rules. Do not include the <style> and </style> tags. Include the {}’s. Don’t use class names if rules apply to whole post, but do include class names (e.g., .entry-title a) for specific elements. Custom styles will not be displayed by the Post Editor.
Define a Custom Field called postclass to add a custom class name to the <article> section that wraps this post.
Post Format Click for help
Weaver II supports Post Formats as shown in the “Format” option box to the right. Click the ? for more info.
Note: when you add settings for the post here, values will be created and displayed in the “Custom Fields” box.”