[Hummingbird] Hummingbird : cannot activate resource optimization

Hi.
I need to optimize my website (because of render blocking resources warnings), but cannot activate resource optimization in Hummingbird pro. Can you help ? I click on the "activate" button, file-check happens, and I'm back to the "activate" button page. I cannot access the advanced mode where I can manage individual resources.
I tried debug mode, no message.