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I've seen that, too, and I do not think, that this stub is relevant for an ID:
If you look at this overview of some Bombylidae wings:
https://galerie-i...ref=155933, you'll find the stubs on several species' wings.
In Exoprosopa: https://galerie-i...ref=354544 you'll see a complete vein instead of the fragment.
Unfortunately I cannot give you a scientific explanation for the phenomenon but I think it has to do with evolution.

Nota bene: I'm still not sure, if B. cinerascens is correct - if you'd add it to the threads title, we would have a chance to attract an expert.