Could be any number of things....
Firstly, how are you tracking the conversions? Just one way, or are there a number of different ways a person can trigger a conversion?
What do you count as a conversion? Is there just one conversion or many?
do you have ecomm tracking activated in Google Analytics? If you do then you may well be getting ecomm data feeding back as conversions, but you might also have AdWords conversion script on your sales confirmation page (or anywhere else in the process)
Another good starting point is to activate the "Conversions" column in your AdWords interface and then segment by conversion name - which conversions do you see?
Take a look and let us know...
In addition of that, you need to also check the attribution model in AdWords Conversion Pixel.
Are you tracking last click or First Click?
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