Hummingbird – Using CDN option lowers the score of the site

I’ve enabled minification on this site and and got a FAIR score on https://testmysite.thinkwithgoogle.com/ then I tried it again after enabling CDN option (I’ve also waited a bit until it runs through all files). I imagined that this should really help even more but I got it actually to lower the score to POOR (on mobile).

This is what I got wit CDN enabled:

MOBILE FRIENDLINESS: 100/100 (Good)

MOBILE SPEED: 62/100 (Poor)

DESKTOP SPEED: 73/100 (Fair)

And this is what I got without CDN:

MOBILE FRIENDLINESS: 100/100 (Good)

MOBILE SPEED: 68/100 (Fair) +6 improvement but it changed from red to yellow

DESKTOP SPEED: 77/100 (Fair) +4 improvement

Is there an issue with that option or a way to fix this? I think this option was introduced just recently and seems it’s still not working properly.

Best Regards,

Rafal