I assume you are in the Xbox Alpha program as I've been having the same problem for the last week and a half. Mixer states they are working on it and said for me to check back with them in two weeks. Hopefully it will be fixed soon as I'd hate to see this current alpha version get released and cripple the Mixer platform for anyone on Xbox. As of right now there is no fix and we are all SOL.
this is not twitch! you can't change the color or you chat or even your bots chat. As for the clear command not working that is beyond my understanding why so you need to open a ticket at http://mixer.com/contact cause staff does not read the forums and you can get better customer service that way. The forums is not really meant for tech support
Do not stream with the Elgato software it's really bad.....
Search for OBS FTL and use that. OBS has many more features than the Elgato software such as your mic only picking up your voice and surpressing all background noise like fans from your mac.
The OBS FTL is mixers version of OBS and will reduce your stream delay to just a few seconds rather than about 30. Your delay will still be about 30 seconds if you view on a mobile device however as Mixer are still working on that.
In OBS you will also need to add a slight audio delay on your mic as it is a little ahead of the capture card video and audio feed. All of this can be done in OBS with no additional software needed.
If you click your icon in the top right it will expand then you can click on Manage Channel, then click the second option at the top to Customize. Finally click your Avatar image to get an file upload option. Note: I had an issue with Edge it wouldn't allow me to select the image and locked up so as much as it pains me to say considering we are using a Microsoft product but try Chrome.