I’m not sure why the history records aren’t displaying, but the domain name change is probably a clue. One problem I’ve seen before is that different PHP versions on different servers can prevent the data from being unserialized. If that’s the problem it probably won’t be possible to recover the old records.
If you don’t see the history appearing as you run new imports on the new domain, though, send me a login and I’ll take a look to see if something else is happening.
Also – the ‘undo’ feature was intended as a way to undo an import immediately if it has errors, not as a mechanism for doing updates of past imports. It may work, but it’s probably better to just delete existing posts from the WordPress admin and then re-import them. Or, store a unique ID in a custom field for each record and run the imports as an update.