I'm pretty sure the latest version (3.16.2.1) is having trouble importing edges from an Excel worksheet that has a space in the name (the name of the worksheet, not the name of the workbook). And yes, I know that the sheet name needs to be enclosed in single-quotes. I believe it also manifests in the MS Excel Import dialog and the behavior of the Adopt buttons for the Source and Target IDs. Workaround is to not have a space in the worksheet name.