What are the symptoms of fake MSGEQ7?

I doubt it - a lot of fakes are rejects or seconds - still work but don't meet datasheet specifications (takes some sophisticated testgear to determine this). If it was the genuine part you need to be aware of a common trick - the first time you order you get the goods, subsequent times its a fake or substitute part of lower value - this plagues manufacturers who have to quality audit every batch made.