Site speed 10x slower since using Hummingbird


I purchased the trial of WPMU Dev yesterday and used WP Smush Pro successfully.

This morning I re-ran the Hummingbird test and my site score improved from 56 to 81.

Then I pressed 'Configure' on the minification section and it said it was 'running the background'. I returned 5 minutes later and now my site takes 20-30 seconds to load (previously took 2-3).

Please could you explain what is going on?