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I think this is likely Monoceromyia javana...see images and comments at this iNaturalist link.

This one from Thailand also looks like M. javana...and is closer to Laos.

Note that some syrphid workers consider Cerioidini as containing only a single genus, Ceriana, and they relegate subtaxa like Monoceromyia and others (that have been long treated as genera) to subgenus status. For those adopting that view, the most informative way to present the name here is as a trinomial: Ceriana (Monoceromyia) javana.