( I'm reporting this too because I think I need high level MNHQ tweakage) . I can't get SN in active convos and baffled. I've been dipping in and out of this problem for ages and it's still not right since last summers der-reg and setting up a new account.
I have gone into customise and chosen SN topics to include and clicked the boxes across. They're still not showing up. And either SN chat or children doesn't appear to be in the options of topics to include 
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IIRC there used to be a blanket SN topic opt in box. But I can't see that either. does one still exist?