Audible Book 5 of Mallorean is still not updated

Audible released new versions of the Mallorean books 1-4 starting last year and stopped at book four in Apr this year. I've been patiently waiting for book five to finally get released with the new narrator? Also reviews state that the old version has quality issues and an annoying narrator so I don't want to waste a credit on it.

The Belgariad has had all five books released with a few months of each other. So I'm perplexed why we haven't seen a Mallorean book five yet. Does anyone know why we're still waiting for a new version?