After Mailchimp made a change to their API, we no longer receive a hard bounced notification. Instead, what Chimpegration Classic needs to do is generate a list of all those sent a communication in your campaign and then identify which ones were identified by MailChimp as 'Hard Bounces'. Once Chimpegration Classic has done this, it can then fulfil the rest of the process.
Depending on the size of your campaign list will determine how fast or slow it is. If your campaign list is several hundred records, you might not notice a change in speed. If your campaign list consists of tens of thousands of records, it will take time for Chimpegration Pro to compile the list for it to search for Hard Bounces.