Yes, this is normal (though in my experience, it's the KLM website that is usually incorrect when it reports the mileage that will be earned, while AF is usually closer to reality).

Are you logged in to your Flying Blue account when looking at the booking online? This is usually the reason why KLM reports the wrong mileage (though it sounds like you are indeed logged in, if it recognises you as platinum).

Are you travelling on a special Air France MINI fare (I'm not even sure if these are on offer to/from LHR)? If so, your attention should have been drawn to the fact that there are no miles and/or no baggage allowance during the actual booking process.

What fare class is the booking in?

And what does the actual confirmation received at the time you made the booking say? This should be accurate.