The only way is, to leave the Family account and re-join again. After the re-join, the first pop-up asks: 'wanna join the family mix?'
Press the 'yes' button and the family-mix works correctly again.
I joined family mix on my PC as the Android app does NOT have the option.
Please be more specific about how to find the Family Mix selections on Android app. I've logged off and back on yet no Family Mix options/selections anywhere.
Thanks for your question!
Make sure to check out this support article, which explains how to access your Family Mix.
Let us know if you encounter any further issues - we'll be here to help you out.
Keep us posted :)