If it could be useful, we separated all the DBs into another machine (MySQL, Mongo, ElasticSearch and Redis).
Our problems with tasks being blocked and wsgi workers being busy for an indefinitely period of time solved by moving Redis to a native environment. Dockerized Redis was unable to manage too many tasks at once and it was creating this issue.
One important note: we have 2 servers, one running the application and the other running the dbs. This prevents our machine from getting out of memory or disk space, as docker consumes a lot and Redis and Mongo also use a lot of memory while processing data.
Hope this will help
Regards