Squares instead of arrows

Hi! I am working on the Zubin Pro and suddenly all the arrow icons on the homepage (from the menu, featured slides, etc) were substituted by square icons. I don't know if the web design team made some changes that occasioned it, but I am not being able to find how to go back to the arrows. You can check the website here to see how it appears: https://covid3d-umfasos.nl/ Do you know how I could fix this issue? Thank you so much! Kind regards, Camila