Hi
This "garbage" is a tag included in the content by sh404SEF to store the meta description and is required to work with Joomla caching. It is an HTML comment and so is not causing any issue.
Just before the page is rendered, it is normally transformed back into a meta description and removed from the page.
The fact that this tag is still present in the final page, and that the OGP tags are missing indicates that the final steps of sh404SEF code are blocked on your site. A likely reason is another extension or your template interfering but it's hard to say without actually looking.
I looked at the page source code and I can see the following:
1 - sh404SEF does not seem enabled at all on that page, nothing from it can be found
2 - The page has a <meta name="generator" content="MYOB" /> tag which indicates something, extension or template or custom code, is injecting a non-standard generator. That something maybe causing the interference.
So as you experience this issue only on that specific site, the 1st thing that comes to mind is compare extensions List and custom code vs what you have on other sites.
If you provide us with superadmin credentials to your website, I can look around but I will definitely need to know what the "generator" tag is coming from.
Best regards
Yannick Gaultier
weeblr.com / @weeblr