I tried to implement Hummingbird on my network but I had some issues. I also enabled the WPMU Dev CDN.
First issue was funny stuff in the front-end, I tried to see if I could fix it, when I could not, I uninstalled Hummingbird. All was good again inside my front-end, but I started having 1 minute + waiting times for any back-end page to open. Connecting .. Connecting - 1 minute +, every page.
I run 6 networks, and I just tested inside all of the other networks, no problem, every admin page opens immediately.
So, Hummingbird must have left something behind ...
Can I get some help here, I cannot work inside the back-end ..