Currently, ShopSync is at feature parity with the original 'Mailchimp for Shopify' app. E-commerce tracking for Campaigns and reporting is available and functional. At the moment, there are a few limitations to note.
We don't think this is good enough; various shopping events could happen inside of two weeks which could be missed. We understand the necessity of having reliable ecommerce tracking, and it is essential that our users can get accurate and useful data in a way to make good decisions for their business. As a result, we're working on something that tracks events for each unique click, versus using Shopify's standard landing page technologies.
MC_CID is short for MailChimp Campaign ID and means there is tracking enabled either on the campaigns or automations which cause these notes to appear. It is how MailChimp tracks the revenue generated by each campaign and an individual list member. Please note, it is sent by Mailchimp through store's connection with ShopSync and we can't disable.