Cannot install 'Dispatch' from site library - php error

Hi,

I'm trying to install dispatch on a local development version of my live site. I know the site library is better used with existing sites, but I'm using a backup to test this. But I'm getting an error than I'm stuck on. When I click 'details' on the Dispatch theme in the Site library I get 4 errors:

Notice: Undefined index: masonry_width in D:\www\Source\wp-content\plugins\gp-premium\sites\classes\class-site-helper.php on line 146
Notice: Undefined index: masonry_width in D:\www\Source\wp-content\plugins\gp-premium\sites\classes\class-site-helper.php on line 146
Notice: Undefined index: masonry_most_recent_width in D:\www\Source\wp-content\plugins\gp-premium\sites\classes\class-site-helper.php on line 146
Notice: Undefined index: masonry_most_recent_width in D:\www\Source\wp-content\plugins\gp-premium\sites\classes\class-site-helper.php on line 146

I have Show Posts Pro and GP Pro at the latest versions. I've disabled WP Rocket. This error seems to me like it might be caused by GP or the site library however...

Any ideas?