Only Heading Displaying

Thanks for the link.

For some reason, your theme sets the font size to zero for testimonials.
https://wpmission.com/screenshots/font-size-0.png

I recommend them asking the theme author what’s up with that.

Meanwhile, try this custom CSS (via Simple Custom CSS if necessary):

.strong-view .testimonial {
  font-size: 16px; /* or whatever */
}