[Wigan Lass]

No. CG brunch is available at 180 plus 10 days like all other dining.

What day was 15 September in your dining booking? If it was actually 180 days, or within about 5 days, this may be why. You are going just as GE opens so it is expected to be very busy. Americans do short stays of up to 5 days by and large, so the first few days of dining and FP booking are always busy. It is better to leave sought after dining or FP to later in the holiday.
I got CG brunch at 6 days and 13 days into my holiday no problem in late October early November, however, someone else booking at 180 days exactly couldn’t get it