I took a look into your portal 5882372 and created an active list to pull contact who has submitted the checkout form (list named - hstest; you can access it by clicking contacts > lists) and when looking at their original source, I do see that there are contacts who are coming through as organic search and paid search.
Looks to me that the bucketing is being captured. In this case, if you could share with me some example contacts, I'd be more than happy to help you identify what's the issue here.
I took a look into your portal 5882372 and created an active list to pull contact who has submitted the checkout form (list named - hstest; you can access it by clicking contacts > lists) and when looking at their original source, I do see that there are contacts who are coming through as organic search and paid search.
Looks to me that the bucketing is being captured. In this case, if you could share with me some example contacts, I'd be more than happy to help you identify what's the issue here.