Outside of what has already been suggested here for QA, which are absolutely some paths I would take, I would recommend checking the sync within Marketo and confirm the synch is active/healthy. Meaning there's no major backlog or errors being thrown.
The order of operations I usually take when troubleshooting a sync error are:
- Does the Marketo Sync User have the permissions it needs?
- Is there a custom sync filter or any other custom configuration in charge of managing the sync? You will need to work with support to confirm if a custom sync filter is sitting between Marketo <> SFDC.
- Is there an issue with the CRM integration within Marketo, what is the last sync date and are there any errors