This post is four years late but i hope that this will help .

It's not necesseraly a django-channels related problem , in my case it's was related to Daphne, it seams Daphne dosn't release the momery after webssocket connections are closed,

Replacing Daphne with Uvicorn resolved the memory leak in my case.

For the diagnosis i'm afraid i don't have much to say, because i suspected many root causes and finaly it was replacing daphne the solution we have adopted