Saved tiddler as HTML/text, tried some CSS styling, inline stuff, etc. Searched around everywhere to no avail. Finally inspected and came to conclusion it was maybe td-border stuff.
Tiddlywiki border. - Image on Pasteboard[pic of border issue]
<iframe src=<<link_here>> style="border: 0;"></iframe>
It seemed like I randomly tried one thing that worked. It was something Eric Shulman had from another unrelated post that I can’t find anymore, but contents subsequently disappeared because I hadn’t figured out yet about saving to HTML/text.