One of the main reason why you are not seeing some or any mix at the time of posting content via chrome browser extension is that the mixes are read-only mixes. tchop doesn’t allow to add/edit anything in the read-only mixes. Please make sure that the mixes in the channel where you are trying publish content are standard mixes. You can check it from the channel dashboard:
If the tag says ‘read only’ - then the mix is read only and you cannot post any content in that mix.
In case of any questions, please feel free to write to us at firstname.lastname@example.org