Hummingbird quintupling TTFB

Hey,

After simply activating Hummingbird on a fresh install (with a blank version of the theme Uncode), the TTFB multiplies by five, from ~600 ms to ~3 s.
This is crazy and definitely not what Hummingbird is supposed to do! Why is this happening and what can we do to stop it?

Also, the support ticket modal is useless – there is no going back if you accidentaly press esc or leave the page for a second – I had to type this ticket twice.. I haven't exactly had a good first meet with wpmudev today.