If the featured image is not getting resized or cropped properly in the Content Grid then there could be the following reasons:
Not an actual featured image
First thing first, make sure the post has featured image set. Content Grid provides an option to get an image from post content if featured image is not set. In this case, custom image size won’t work.
Outdated version of WordPress / Beaver Builder / PowerPack
Please check whether you are running the latest version of WordPress, Beaver Builder, and PowerPack or not. Update them to the latest version and check if it fixes the issue.
Actual image is small than the registered image size
It is possible that you’ve uploaded an image which is dimensionally small than the registered custom image size. For example, you are uploading an image of 770×460 dimension and the registered image size is 1200×660 in dimension than the image won’t get resized.
Broken image size data
In some cases WordPress is unable to serve images for custom image size since it’s not getting the path of resized image. In this case, you can use Regenerate Thumbnail plugin to perform the image resize process.
Using any Image Optimization plugin
Sometimes image optimization plugins serve the images which are intended to fit the container size. In this case, you can try disabling the plugin or disabling the image optimization feature of a plugin (like Smush or JetPack).