I believe that there's some place that sets a default sphere or bin size to be the dx of the center cell, but I have no idea which machinery you are moving through to get to this point in the profile. Could you decorate the __init__ method of BinnedProfile2D with @print_tb (defined in yt/funcs.py) and then send at least one representative traceback, so we can look at each part of the stack and examine the neighbroing code?
Here's the traceback when I decorate BinnedProfile1D (which is what I'm using):
And here's if I decorate BinnedProfile1D.get_bins():
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