Good evening Nic and welcome back!
Thank you for reaching out to us.
I would love to help you with this topic.
What is going on is that the customization you have done uses your WordPress site’s thumbnail format (150×150 px), but the image has a width 100% CSS rule that re-sizes the thumbnail to 240×240.
This is why the image is blurry. My recommendation would be to either:
- Tweak you customization to use a different image size than thumbnail (e.g.: medium)
- Run a thumbnail regeneration plugin on your site after changing your WordPress thumbnail size setting to 240×240 px
Let me know if that helps.
Have a great day!
Geoff B.