I’m currently testing ERPNext on a VM as a possible alternative to our current ERP system. I started with v12 of ERPNext and started importing data. However, I had massive problems in v12 but managed to create workarounds by essentially creating new data first with minimal entry then updating these data with desired entry. When using v13, that method does not seem to work. It worked for suppliers, worked on some of the companies where the rest I had to create manually and none of the items.
On a side note: I also think it would be of great value to have a pop-up message showing the progress of the import and the approximate time remaining.