On a very large website I have changed the permalink structure, for technical reasons. Every URL is 301 redirected to it's appropriate one.
A few days after the change I have noticed a drop in organic traffic of over 60%. Also in Webmasters Tools old URLs appear with duplicate titles and descriptions of the new ones.
Should I ignore the traffic for now? Is it normal to have such a big drop?
I presume it is because now Google thinks I have thousands of duplicate pages?
If this is the case, how long does it usually take until things go back to normal?