If the debug option is active, it is possible to see the data from the logs viewer, or in the files inside the folder var/logs/sl_logs/ (in Magento installation). It includes info from the imported content, the evolution of the synchronization, the time required, etc.
For example, a message like the following:
Indicate de ID of the element in Sales Layer, since as it could not be generated in Magento 2, we do not have its ID.
We will have to find the item in Sales Layer and correct the problem that the message indicates.