Stars not showing up when logged out of site

I've noticed that the stars on my reviews shown on the website front end are showing up as boxes - like the star icons aren't showing up. When I'm logged into the website, they do show up, but when not logged in, they're showing up as boxes.

I've tried excluding wprev from the NitroPack cache and cleared that and our WPEngine cache as well, but the boxes still show up.

Anyone else had this issue?