Can’t start an import

I recently installed this and tried to use it to import several sets of data (posts, users, comments) from a different database system. I started off my testing with just five rows of data to come in as posts of a custom post type with some custom fields. These tests worked as I adjusted my source data to be compatible with WordPress. When I was then ready to bring in the full set of rows (under 600 and just 7 fields), I found that the file seemed to be parsed fine in step one but that the preview data feature did not work and I could not assign fields. It behaved as if the file was empty and I was unable to import anything, even with my saved import configuration.

I kept trying different things including smaller sets of records but nothing would make it work until I named the new file the same as my original test file (“events-sample.csv” instead of “events.csv”). Then I could see the field names and preview data and successfully complete the import.

A couple of days later and now I’m trying to bring in a table of new users (less than 200) and I’m back to the same problem again. The file appears to be accepted and scanned successfully in step one, but no field data or field names show up in the subsequent steps. I tried the same trick of renaming the file but that didn’t help this time. I tried uploading the file to the plugin’s uploads directory and I was able to select it but still no fields or data. I tried uninstalling the plugin (with plugin data deletion) and reinstalling but still no go.

What’s the trick to get this to work again? (I’m running WordPress 6.4.3, PHP 7.2.21. This data migration is part of the process of getting ready to update my server, including PHP.)