Try adding the rule named "Flash Sale" with simple calculations and triggers... just one line, make it as simple as possible so that hopefully it will apply.
Then manually go into the cart object .php file and update the rule manually using the code I've provided below:
//eCart Rule
function WAEC_eCart1_FlashSale() {
$totalDiscount = 0;
if (true && (($this->InCart("1") == true) || ($this->InCart("2") == true) || ($this->InCart("3") == true))) {
$totalDiscount += ($this->TotalColumn("TotalPrice") * 0.15);//Result
}
return WA_eCart_FormatNumber($totalDiscount, $this->ForceDecimalsC, $this->DecimalPlacesC);
}
//eCart Rule