In function gutenberg_form_node_form_alter on line 765 we are setting the available image-sizes:
$form['#attached']['drupalSettings']['gutenberg']['image-sizes'] = $sizes;
This throws a warning:
Warning: Undefined variable $sizes in gutenberg_form_node_form_alter() (line 765 of modules/contrib/gutenberg/gutenberg.module).
Ideally to be safe we need to initialize the $sizes array before using it.
Add the following line before the code that populates the $sizes array:
$sizes = [];
On the other hand, I'm not sure where the image sizes are defined in ['gutenberg']['image-sizes']
Fixed
3.0
Code
Automatically closed - issue fixed for 2 weeks with no activity.