No captions for images in my gallery

Site URL: https://cello-seahorse-fw8x.squarespace.com/config/

I am setting up our art gallery's website and when using a gallery grid, or any grid, I cannot create a caption. When I click to manage the gallery images it offers the "add a description" but there is no save button and when I click back on it it's gone.

In addition, unlike adding an images section there is no option to place a caption under the image. I'm only using gallery grid for the convenience of creating rows that are aligned and formatted. Also, adding images using an images section gives me the option to use the "Dark Overlay" theme for lightbox, I prefer this but I don't have that option with gallery grid, on a desktop once an image is clicked the background bleeds through a white translucent lightbox which doesn't look good. 

Click on artist page Agapito Labios as an example of my issues. Compare that with the Bob Franklin page (alphabetized by first name under Featured Artists) which is how I prefer (captions and dark overlay lightbox)  it but it's much harder to align and format this way because I have to add individual images and resizing them is a pain because when I shrink one image the other gets larger as a result etc.

I did get custom code to reduce the space between images and captions as seen in the Bob Franklin page and that helped.

If possible I need both captions and the ability to have the dark overlay theme for lightbox. Thanks!

Password to view: TXsouth61

Checking again. SS team updated caption for Gallery in SS 7.1