Are the subscribers in your Mailchimp account not syncing with SparkLoop?
The most likely cause is that one or more of your custom fields in Mailchimp is marked as required.
You can see if your Mailchimp list has required custom fields by following these steps:
Go to your Mailchimp account > audience and select the right list (also called "audience")
Click on Manage Audience > Settings
In the Settings page choose Audience fields and *|MERGE|* tags
Make sure that NONE of the custom fields is set as required. In other words, the column Required? should be completely unchecked.
After you make your custom fields not required, all subscribers who were not synced will be automatically resynced by SparkLoop. This might take from a few minutes to a few hours (depending on how many subscribers you have and other factors) but they will be synced eventually.