I just had a chat with a FB agent on the phone after my latest domestic flight booked in O class was credited with 0 miles.

After consulting FB system it appears that from May the 16th rules have changed regarding AZ domestic flights. Here are the classes which allow, from now to earn miles:

R = 25% miles flown
N S Q X W = 50% miles
K V T M H B Y = 100%

With a FCO-LIN in R class costing 215 euros, earning 25% miles is becoming very expensive.

Of course, the FB website has not been updated since the changes.