I had the same problem as you, and after trying almost everything I found where was the problem.
To add your user PI to GPIO group, in the module page says to run:
sudo useradd -g pi gpio
My RPI always replay me that GPIO group already exists… so nothing happend
I solve it by running:
sudo usermod -a -G gpio pi
In this case pi user is added to gpio group
I just restarted and it worked.
Now using the following command:
gpio readall
I can see how the Inputs and Outputs change
I hope it works also for you