It’s a real worry, particularly in a small town, a small profession, or a small community — and particularly in identity-specific and language-specific groups, where the pool is by definition narrow.
What screening already does
Group composition is deliberate. A leader building a group is thinking about overlap, and the screening conversation is where they ask about it — sometimes directly, sometimes by asking about your work, your neighbourhood, or your community.
This is the moment to raise it. If there’s a specific person or a specific circle you wouldn’t want to encounter, say so. A leader can’t tell you who is in the group, and they can check and tell you whether the group would work for you.
That conversation is confidential and it’s a routine part of the job.
If it happens anyway
It does, occasionally. Someone joins later, or the connection isn’t obvious until week five — a colleague of your sister, someone from your child’s school, a person you dated once.
Tell the leader immediately, outside the session. Not the group first. The leader needs to handle it and they have done it before.
The usual outcome is that one of you moves. Not because anyone did anything wrong — because neither of you can use the group properly while the other is in it. A group only works if people can say the thing, and prior connection reliably prevents that in both directions.
Which one leaves is usually decided by who has been there longer, and by what other options exist. Good leaders will find the other person a place rather than simply removing them.
The cases where it can work
Rare and worth naming. A very distant connection — someone you’ve met twice at a large event — can sometimes be workable if both of you raise it, both genuinely want to stay, and the group knows.
The condition is that it’s named out loud in the room. A connection that two members are quietly managing is corrosive to the whole group, because everyone else can feel that something is being handled and nobody knows what.
The related worry
Not knowing someone, but being recognisable — a public role, a small profession, an unusual situation.
That’s worth raising at screening too, and the honest answer is that members are bound by agreement rather than by law. For some people that’s a reason to choose an online group licensed in their state but centred somewhere other than their own town — which is one of the underrated advantages of the format.