CircuitHub works best when your Altium database (design files) has unique, consistent, internal identifiers. Altium uses multiple names for these identifiers, but the name most relevant for CircuitHub purposes is "Component Links".
To test, select Design-->Update PCB Document from the menu while you have your schematic document (SchDoc) active:
If you have an ID inconsistency or duplication you will see a "Failed to Match" message when you attempt to push a netlist from your schematic design (SchDoc) to your PCB Layout (PcbDoc). Exit the "Failed to Match" dialog using the cancel "X" in the corner. If you press "Yes" or "No", you will proceed with the ECO process and that is undesirable at this time (we want to fix the problematic ID's first).
Open the PCB layout (PcbDoc) and use the menu: Project --> Component Links
In the Component Linking interface make sure that the horizontal lines have designators that match, select the first item in each box, and then press the ">" button for each matching line until the "Un-matched Components" list is empty. Note: there is a way to do this in one-click via the filter system at the bottom of the interface window, but it was unreliable in prior versions of Altium.
When all of your identifiers are correct, the interface will look like this:
You must click "Perform Update" to write the changes back to the schematic and PCB documents. If you close out of the interface without this action, the updates will not take effect. You will receive a confirmation dialog prompt indicating the the changes have been successfully written to the respective files.
You can now perform a design update without issue and import your files to CircuitHub for a fast and accurate fabrication experience.
Special thanks to Jonathan Friedman at Assembly for authoring this article.