Rewards arrived in-game but not in my inbox

Posting this mostly so the next person searching finds an answer. It behaves as expected on one account and not on another, same device.

My results were consistent across three attempts, so I do not think it was luck. Interested in the counter-argument if there is one.

Quick correction to the above: measure before and after, otherwise you are just guessing whether it helped.

Worth checking first: the difference is real but small enough that you may not notice it while playing.

Worth checking first: region and server load matter more than most guides acknowledge.