MySQL UTF-8 Encoding Problem
Not an "answer", but steps for debugging...

All of these need to agree:


 tag on HTML
character_set_client, character_set_connection, and character_set_results
the WP setting (I don't know what is, try this?)
the CHARACTER SET on the columns of the relevant tables, or if nothing mentioned, then on the table, from which the columns inherit.
And the connection user should not be root.


If, however, the data is already stored in the wrong encoding, the problem is messier.  Do analyze this, do SELECT HEX(col), col ... to look at some particular thing that is causing the black diamonds (etc).  Show that to us, plus list the other things; then we can proceed.