Update from my side:
I have to say that I decided to take part in this promotion by the end of July, so most of transactions are made in August.
Avios received on my IB+ account so far:
- Iberia Cards - monthly avios credit, with each bill;
- Cabify - credited really fast;
- Repsol - fuel in August;
- Cepsa - fuel and in-store purchases, two separate transactions, both appeared;
- Parador - Tarjeta Una Noche (transaction in August, credit after 2 chasing emails);
- Cinesa - watched a film in August);
- Chic Outlet Village - went to do some shopping in August);
Still waiting to show up:
- IberiaPluStore - appear as pending in IBPluStore;
- Hotel booking via Iberia.com - booked and stayed in the end of August.
- El Tenedor - went in the end of August. According to the small print, avios will be credited within 2 months - by mid-end of October.