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Hey Kit - This is a question I am seeing coming up a lot recently! I think you'd be well guided to either get in and do a deep analysis on your own site or hire someone to do one to get to the bottom of this. There have been a decent few people sharing some screenshots of Search Console (Barry rounded them up here) where some saw drops, others saw steady, and still others saw increases. The results you see from AMP seem to heavily depend on the correct technical implementation (and Search Console shows you errors) as well as the type of SERP feature you are in (regular organic, carousel at the front or buried deep, etc). Hope that's helpful. John