I might be a little late to the party, but gonna throw this out there anyway: I recently had a similar shifting problem on a bike that I pulled the spindle out, but it back in, long side to the chain rings which made sense to me and had similar symptoms you are describing. So if they have the spindle in backwards, that might be the problem. In my bikes case, the weird part is the ND side crank is out 5mm farther than the DS crank.
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