During the building of these units multiple things have gone wrong.Issue with 015 then?
Including screws and nails been put through wiring looms. Wiring looms too long for where they are fitted then causing thermal events, Glue coming loosing holding parts down, etc etc
It will all depend on how much rectification work each unit has needed doing.
015 may need more work than 016.
Unit 017 has not been seen as a complete unit outside where as 018 has etc.