HI Brady,
Maybe one of your extra installed extension cut it off. or it's just a cache issue ! sorry, I am guessing...
Anyway, I made quick test on my own site, and HTML code was OK, later I made the same test on yours site (link below) and as resoult I got correct code
<a href="/why-3d/travelblog/3d-travel" rel="nofollow noreferrer noopener" id="btn-a645f856" class="sppb-btn sppb-btn-custom sppb-btn-lg sppb-btn-rounded">Button</a>
with all rel options that I checked. You can play with the same page "Button Addons Test" as I did.