Thank you jafolkerts, fanatic26, je_mario, KWMiner, LENIN12345 and Sandal_Hat for your responses.
I had a few miners from my last batch with that issue. I rolled the firmware back and they all came up within 15 minutes.
The firmware I used was Antminer-S9-all-201704280713-autofreq-user-Update2UBI-NF.tar
I tried to install the newest firmware (last row of the table in the link bellow) and I couldn't connect to the pool. Then I installed the one you recommended (first row of the table in the link bellow) and I was able to connect. However one of the fans (the front/intake fan) stopped being recognized, it does not even spin, and a fan-related error appeared in the Kernel file.
Does anyone have an idea on how to solve the fab not being recognized problem?
Best regards,
Paulo
Link to firmware:
https://shop.bitmain.com/support.htm?pid=00720161126080548570Q2tDBXAH065D