Mark,
Sorry for the delay. Usually, the problem you mention is specific CSS issue. In your case, it was a new CSS style we hadn't seen causing issues before. I'm not sure of the exact name of your template CSS files because you have some compression/optimization stuff going on. However, I'll tell you what I can.
The problem file is: templates/rt_leviathan/css-compiled/master-c3476a32df433a224bc90d2454fc6e3b.css
The problem style is:
iframe, svg {
max-width: 100%;
}That's causing the Like button iFrame to not expand beyond the width of the Like button itself when the comment box opens up.
Hopefully that's enough info for you, but if you need more help, please disable your compression/optimization plugin and let me know.
Thanks,
Alex