Most of the time when emails do not get through to the intended destination they have been redirected as junk or blocked by the email provider in some way.
I am not saying that is the case here but failing to send an email to one possible recipient is kind of far fetched. I can not conceive of any reason for Roku to block one customer from receiving their emails.
Again, what offer are you specifically referring to? Yes, I know you'll say all of them. But what offer this time?