The question is essentially summarized in the subject line.  I'll add that I'm working with Cognos v11.2.3.  

At first, I thought the custom skin we created might have introduced the symptom except that skin is only designed to influence the Welcome page.  

I'm seeing blurry text all across the Cognos Analytics UI including in the Reports, Dashboards, and Stories authoring tools too.

I am convinced that the IBM Plex fonts were not specifically loaded onto the impacted server(s).  Is there a likelihood that loading the IBM Plex fonts will resolve this symptom?

  Thanks for sharing any guidance or hints.

Can you paste in a screenshot? Also, I'd be interested in seeing what this looks like in the dev toolbar. Press F12 or Ctrl-Shift-I to open the browser dev toolbar, then use the element selector to select one of the blurry text elements. On the right pane click on computed and scroll all the way down. This will show the actual font being used for that text element. In the below example we can see that "Recent" is using "IBM Plex Sans SmBld".