James, Just emailed you this message: ‘Just a simple thought but, normally, it’s a good idea to have a little tension when locking the halyard in as it’s otherwise easy to pull it a fraction too far so that it easily releases. I always hoist the final few inches by pulling the halyard at the same time as pulling down on the luff then when it clicks it’s in the lock.’
Sorry I didn’t respond sooner but not always monitoring the forum.