A recent update to LifterLMS changed the CSS selectors that are used for the borders that appear around the instructor image on course pages:

You can fix this by adding the following to your child theme stylesheet or Divi > Theme Options > General > Custom CSS:

/* Instructor Image Border */
.llms-instructor-info .llms-instructors .llms-author {

   border-top: 4px solid #43BFB4;

.llms-instructor-info .llms-instructors .llms-author .avatar{

   background: #43BFB4;

   border: 4px solid #43BFB4;

Please remember to update the hex code values to the color you prefer to use, and to clear all caches.