MySQL same table calculation wrong results

You don't include the table alias in count(*).

Once you fix that problem, you'll see that you have an alias problem in the subquery. I think the subquery alias should be t2 rather than s:

SELECT c.idx, c.club_name, s.sale_event_date, COUNT(*) AS total_guests, 
       (SELECT COUNT(*)
        FROM sales t2
        WHERE t2.qr_scanned = 1 AND t2.sale_event_date = s.sale_event_date
       ) AS total_scanned_guests, 
       SUM(s.rep_sale_commission) AS total_rep_commission, 
       SUM(s.sale_commission) AS total_admin_fees
FROM club c LEFT JOIN
     sales s ON s.club_id = c.idx
WHERE c.admin_id = 37
GROUP BY s.sale_event_date
ORDER BY sale_event_date DESC;

In fact, I don't think you need the subquery at all. It looks like you just want conditional aggregation:

SELECT c.idx, c.club_name, s.sale_event_date, COUNT(sales.club_id) AS total_guests, 
       sum(s.qr_scanned = 1) AS total_scanned_guests, 
       SUM(s.rep_sale_commission) AS total_rep_commission, 
       SUM(s.sale_commission) AS total_admin_fees
FROM club c LEFT JOIN
     sales s ON s.club_id = c.idx
WHERE c.admin_id = 37
GROUP BY s.sale_event_date
ORDER BY sale_event_date DESC;

Change

COUNT(s*) AS total_guests

to

COUNT(*) AS total_guests

or to

COUNT(s.id) AS total_guests

At least that seems to be your immediate problem.