If it's not arrived and not in your spam folder, I suggest something went wrong. It literally takes seconds for the confirmation.
But as someone mentioned, you can also complete it at the airport on arrival, or try again on the plane, if you have connectivity. Just triple check all of the information, passport number, etc.
Ultimately, it's all up to the IO. Best to have the material available, if requested, but generally it's not. No point in arguing with theories here about it, and even less with the IO.
The DTV has been granted way too softly, so it's possible they're looking to get a bit stricter with checks. Nothing will be consistent.
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