Feedback after synchronization
If the debug mode is active, the files _debbug_log_saleSales Layerayer_timers_{date_time} will show the total time required for the synchronization, and also the time required for some subprocesses for those items.
Managing errors
In order to activate the debug mode, the file settings.php in the Sales Layer plugin must be edited. Here, the parameter Sales LayerYR_WooCommerce_DEBBUG must be changed to 1. From that moment, the logs folder (inside the plugin folder) will include the different files with the logs of the imported info, the synchronization, the time required for the process, etc.
Note: It is important to avoid having this option always active. The logs aren’t deleted automatically and they can use a lot of disk space.
For example, an error like the following one:

Shows only the ID of the item in Sales Layer, not in WooCommerce as the item hasn’t been generated there. In that case, the next step would be to look into Sales Layer to check what is happening with that item, using the info provided (“category parent not found”).