I just installed Porto theme (v. 5.1.1) on my local installation, within Wishlist 3.0.2 and latest WP / WC
I can reproduce the issue with icon/button, but I think that it is realted to theme customization
In order to solve it, I applied some changes to the following file inside theme folder: wp-content/themes/porto/woocommerce/add-wishlist-button.php
You can find updated version of the file here: https://we.tl/t-VeXcqTqc7V
Here you can see my final result: https://www.screencast.com/t/OhvkiKxI2
Could you please try to update the file and let me know if this solves appearance problem?
Don’t forget to make a backup copy of original file before proceeding, and always test on a staging environment
If everything works, please consider contacting theme developer, and ask them to update template they override within the theme (I suppose they will anyway release a compatibility update soon)