Originally Posted by PR-Giants

You have more information about what you're doing than any of us here because we're only looking at your photos. In my opinion that substrate is not suitable for that plant at it's current state of development. If it was a bare rhizome planted a week ago the root development would be considered good but the fact that it was planted in June makes the root development terrible.

Here's a photo from a 2014 study I did on mitigating rhizome rot in A'ea'e. The rhizomes were grown in an extremely dry substrate while the roots were allowed to grow in an extremely wet substrate. What someone notices about my photos might shed light on what's going on in your situation.