After trying the above suggestions, the only thing that worked for me was changing the border attribute to "0" in the following sections of a child theme's style.css (do a "Find" operation to locate each one -- the following are just snippets):
.comment-content table {
border-bottom: 1px solid #ffffd;
.comment-content td {
border-top: 1px solid #ffffd;
padding: 6px 10px 6px 0;
}
Thus looking like this afterwards:
.comment-content table {
border-bottom: 0;
.comment-content td {
border-top: 0;
padding: 6px 10px 6px 0;
}