So about 5-6 times now DD (11 weeks) has done this: latch and make a grossed-out face (2-3 times) latch and GAG. She'll do the whole routine a couple times and go on to nurse as usual.
When this has happened it always on the same side, when that side is offered second and if she is tired (last feed before bed, first in the morning). I don't think I have a fast let down, she isn't choking, it is like she has stuck something too far down her throat.
Today when she did it she was "talking" the whole time so I just sat her up and she skipped the second side (which is rare).
It isn't anything I am worried about, just something I have never had happen before; I hope it doesn't turn into an issue.