This happens when some Pending conversions for an offer are exist. The FuseClick system actually records the conversions the Pending conversions however, they are shown only in the Conversion Reports but not in other reports. The pending reason may be because of the traffic coming from out of the allowed countries.
There are 2 ways to approve pending conversions for an Offer:
(1)   Approve the conversion manually by clicking on the Approve button against the conversions list.
(2)   If you don't want to approve it manually, you can go to Setup -> Tracking Settings -> Set "Conversions out of Allowed Countries” option to Approved. The traffic coming from out of the Allowed Countries will be approved directly. You can view the conversion message in conversion report.

Even after following above 2 methods for approval of Pending conversions, if you still find there is a mismatch between the conversions recorded at Advertiser and FuseClick system then, please contact us.