After you install Trellis, if you notice the Featured Image Size setting in the Mediavine Trellis > Display section is not affecting your Featured Images for your Latest Post page, Category pages, and post pagination, it means you’ll need to Regenerate the Image Thumbnails.
This happens when we change themes because image dimensions that are available in your new theme were likely not available in your previous theme.
Luckily, there is a pretty simple way to resolve this issue thanks to plugins like Regenerate Thumbnails.
Note: If you’re running the Shortpixel plugin, you’ll need to use the Shortpixel-specific regenerate thumbnails plugin instead. This help article will walk you through using the Regenerate Thumbnails plugin.
> First, Install and Activate the Regenerate Thumbnails plugin from your Plugins > Add New page
>Go to Tools
>You only need to regenerate thumbnails for Featured Images, and this process can take some time, so you’ll want to leave the “Skip regenerating existing correctly sized thumbnails” setting checked.
>Then click Regenerate Thumbnails For The Featured Images Only button and leave this tab open while the process is running.
Once this process is complete, you can navigate to the Customizer > Trellis > Display settings and choose the Featured Image Crop that works best for your site: