I checked our logs and found that you seem to be encountering a large number of the following error.
Save Warning: The Customer/Employee/Vendor/OtherName could not be sent to QuickBooks. This Name is already in use. Please edit the Name so that it is unique and save again.
It could be that your code is attempting to do everything twice, but isn't setup to handle errors correctly. Therefore, even after failing to insert the entity, it still inserts the opportunity and activity creating a duplicate for the existing entity.
Hasan - I'm happy to check our logs for you as well. I'll just need your company account name in order to do so. Feel free to shoot me an email with this.
I hope this helps.