When syncing an expense to Xero sometimes not all the attachments are uploaded. This could be because:
The attachment's file type is not supported by Xero.
You have more than 10 attachments for one expense. Xero does not allow us to attach more than 10 files.
The receipt wasn't properly uploaded into Expend.
The expense may not have a receipt uploaded yet.
After resolving the problem, you can retry the synchronisation by clicking the Sync button on the expense.