Connect Eloqua with GoToWebinar and setting up

Dear Community,

After the success of the integration of GoToWebinar with Eloqua, we have created a webinar on GoToWebinar.

We wanted to send invitation email with Eloqua, with an Eloqua Landing Page and a registration form. 

Each form registration was supposed to pass on the data to GoToWebinar, to receive recall email one day before the event. 

We have connected the N° of webinar to the campaign in Eloqua. 
We can see all registrations in the submission form in Eloqua, but there is a big gap between registrations (Eloqua:69 versus GoToWebinar:28)

I've tried to reach the call support but they can't answer me why there is this gap.

Thank you for your answer or anything that could help.

Felix