The issue is still being investigated, but we have a workaround:
Access the Linked Data Source page of your app
From the Actions button of your data source, choose Edit Data Source Configuration
Toggle the MongoDB Connection String switch, Save the configuration, and Deploy, waiting for it to be successful
Going back to the Sync page, the Terminate and Enable buttons should now work, and the Deploy button should appear again: the flag that you had activated to force the deploy (wireProtocolEnabled) should be set back to false, so you shouldn’t need to go back to the Data Source to restore it, but double check in case.