Page List - An Error OccurredBrowser Info Environment
I couldn't recreate the error on my localhost. Will you check your C5 log section and see whether or not a whale-gallery related error has been recorded. Filling up the environment section of your ticket also might help. You may get the error on a specific version of PHP, C5, or Gallery add-on.
Error in the logs is as follows:
Exception Occurred: /path/to/web-root/www/packages/whale_grid_gallery/blocks/whale_grid_gallery/controller.php:622 Class 'Concrete\Package\WhaleGridGallery\Block\WhaleGridGallery\CollectionKey' not found (0)
C5 = 8.4.4
PHP = 7.2.17
Happy to PM you credentials to access the site if that helps.