Can not update galleries once created

When I go to edit the gallery, whether it was created in the page directly or created in the Galleries section of the plugin, I get “Updating Gallery Data” and the Items Manager just keeps flashing “loading”. It cannot retrieve the images. This is happening on all my websites. I am currently on a test site with only Generate Press theme and the Simply Gallery plugin installed. I tried backing down to previous versions and the same thing is happening. The only solution is to delete the gallery and start over but once you save, you can’t update anything.

Thanks in advance!
Debra