Different experiences
FYI.
I live here in Vietnam, am now a VN elite member (December 2020), and have had quite a few experiences with VN. Mostly good.
Everything must be handled by email or in person. Over the phone... It is always a different department.
The app is poorly designed, riddled with bugs, often out of date, and inconsistent. But it is relatively easy to use, and does have a few nice features.
If I upgrade a flight, (with the cheap upgrade offered 24 hours before departure), it is guaranteed that I cannot check in online. You can upgrade after check-in, but then you just get reissued your Y class boarding pass.
I was double charged twice, and on both occasions after reporting it to ticket desk at airport I was refunded same day.
If in C class the service is generally outstanding, Y class is below average. On board Bamboo Airways is better.
I do now only fly VN and not the low costs because often VN is actually cheaper, and certainly more reliable in terms of delays. VietJet & Bamboo often have horrendous delays, and on top of that they frequently change flight times. Not by minutes, but by hours. I would say that its quite normal if I book more than a month ahead to have at least 3 flight changes.
It does happen on VN too but less frequently, and I normally get a phone call advising me of the change.
The lounges are barely adequate, and feature some very strange things, like plastic wrapped slices of bread. Bamboo's lounge in Hanoi which you can purchase access to if not entitled is the best lounge in Vietnam. Staff there will barely let me carry a can of coke back to my chair.
Updating of my FF account is totally random from next day to 10 days delay, but usually 2 days, so I doubt it is automated.