My latest tests have brought me to a theory on this.

If a database has phone numbers in it that are longer than the field, that is greater than 20, then the import fails and does not complete.
Earlier versions were tolerant of this. The message shows: Too long string during import.... but after a number of these the import fails.
I have increased the length of the telephone number fields in hal I did them one by one, until all the messages cleared and the import completed, almost, it still crashes very near the end. So the database is still not sound.
I am assuming that normalised telephone numbers or something else that may have changed to cause this.

I am now trying to reconfirm this in my other database, I am aware that they have some long values, these may be be in other fields, I will check