OP give more context in one of the child comments: > Our founder asked me "Is there anything we're sending over the API that might clue someone in when someone

OP give more context in one of the child comments: > Our founder asked me "Is there anything we're sending over the API that might clue someone in when someone signs up? Are we sending a createdAt field or something?" and I said "No, but we do have a timestamp in one of the IDs..." -- well, we removed the field and this behavior stopped soon after.