Never happened to us, but since you've got no reply still, I dug in online a bit and found this
Which basically means one of the most probable reasons is that "not all clicks and their associated click cost are eligible for conversion tracking reporting. As a result dividing the cost column by the conversions column might return different numbers to what you see in the interface. The most common reason that a click wouldn't be eligible for conversion tracking is if the system is unable to track the cookie (due to the browser or device used e.g. low end mobile devices). These clicks will be removed from the cost/conversion calculation."
Also, check your billing, to see what you exactly paid for and if there were any invalid click activities
I really hope it helps!
Thank you
I found the problem and it is a big one at least for me as it has cost me £3500 so far in clicks without any conversions :
Automated extensions
Adwords have these enabled by default for my account without any notification. You can see how much they've spent by selecting "Segment" / "Click Type". The clicks show as "Sitelink".
I've disabled them now and so far today everything looks fine.
Do not show specific automated extensions for this account:×Automated call extensions
×Automated location extensions
×Dynamic structured snippets
×Dynamic callouts
×Dynamic sitelinks
×Seller ratings
×Longer ad headlines
×Previous visits
×Consumer ratings
×Automated app extensions
I'll try to get a refund for those clicks from Adwords as I didn't even know about this new feature , neither have I been notified about it or agreed on using it.
Don't know if I'll have any luck with this but it's worth the try.
Hope this helps other people avoid this costly mistake.
Sometimes after a few days it corrects itself as system is not perfect.
Another aspect could be your conversion tracking is not one to one however one to many check your conversion tracking setup.