During import Nominatim detects deadlocks (before it used to crash). It's possible the detection logic simply got better. If I remember correctly it does string matching.
Check `SELECT indexed_status,count(*) FROM placex GROUP BY indexed_status;` in the `nominatim` database, database after the import, all records should be `0` (zero). You didn't say that the import stopped so I assume the import finished fine.
(zero).
Nominatim 3.1 puts postcodes in different tables. https://www.openstreetmap.org/user/lonvia/diary/43143 On a planet database 10GB is less than 5% difference and expected.