I didn't notice this issue in the past until now... not sure if it's a recent update that is causing it but I get duplicated site titles on my sites.
In Infinite SEO, my home title setting is "%%sitename%% | %%sitedesc%%"
What gets displayed is:
"%%sitename%% | %%sitedesc%%" | %%sitedesc%%"
I also notice that the Facebook Open Graph meta "title" tag description part is also duplicated...
For instance this is shown:
<meta property="og:title" content="Site Title | Site Description Goes Here | Site Description Goes Here" />
Nothing is wrong with the og:site_name though.