Alfine crank 1x9 setup, spacer issue
I found the solution!

I've bought an alfine crankset with inner + outer chainring (FC-S501 GCx2) instead of of an alfine crankset with only the outer chainring (FC-S501 GCx1). 

The problem being that the FC-S501 GCx2 is designed with a 49.2mm chainline and the FC-S501 GCx1 with a 42.7mm chainline.