"Also note, (see bug below on bottom of page); If you are using the FreeSWITCH pooled resources, then you definitely need Threading = 0 for high call volume. What this does is it "disables a global mutex in the ODBC core that only allows 1 concurrent operation per process regardless of the concurrent connections." (i.e. It slows down when you have too many connections trying at one time)"
Let's see if this actually helps. It could be that Threading=0 is default in unixODBC version 2.3 and that is why changing to that version resolved that issue.