I had similar situation when applied in Hanoi. I was on Non B visa and had re-entry permit so knew I would have to cancel this anyway.
Left after 5 days in Hanoi and approval was emailed 2 days after. I then canceled work permit & Non B visa and did a border bounce to activate DTV. No issues coming through immigration on either occasion fyi.
where does it say that in the ‘rules’ mate? It states that you need to apply in x country but not that you need to be there when DTV is issued. Obv talking online here not in person applications