Hi Andy ,
Thanks for the link!
It seems like there's a custom CSS that's increasing the font-weight of the icons.
Try to use this custom CSS to revert it back to the normal font-weight:
.buttonizer .buttonizer-button .fa-line {
font-weight: 400 !important;
}
Simply paste this into WordPress' Additional CSS in Customize
Please let me know if this works for you! 😃