The quote svgs were moved to a new directory but it seems the CSS paths were not updated.

I found below and the correct path is

../../assets/public/svg. Other svg may have same problem but the quotes are the ones my site uses.

  .wpmtst-testimonial-content:before {

    left: -56px;

    top: 0;

    -webkit-mask: url('../../public/svg/quote-left-solid.svg') center center no-repeat;

    mask: url('../../public/svg/quote-left-solid.svg') center center no-repeat;

  }

  .wpmtst-testimonial-content:after {

    right: -56px;

    bottom: 0;

    -webkit-mask: url('../../public/svg/quote-right-solid.svg') center center no-repeat;

    mask: url('../../public/svg/quote-right-solid.svg') center center no-repeat;

  }