fix(mixed-timeseries-plugin): Second query stacks stacked on top of first query series (#29119)

superset-frontend/plugins/plugin-chart-echarts/src/MixedTimeseries/transformProps.ts

@@ -392,6 +392,7 @@ export default function transformProps(
         seriesType,
         showValue,
         stack: Boolean(stack),
+        stackIdSuffix: '\na',
         yAxisIndex,
         filterState,
         seriesKey: entry.name,
@@ -438,6 +439,7 @@ export default function transformProps(
         seriesType: seriesTypeB,
         showValue: showValueB,
         stack: Boolean(stackB),
+        stackIdSuffix: '\nb',
         yAxisIndex: yAxisIndexB,
         filterState,
         seriesKey: primarySeries.has(entry.name as string)

superset-frontend/plugins/plugin-chart-echarts/src/Timeseries/transformers.ts

@@ -151,6 +151,7 @@ export function transformSeries(
     areaOpacity?: number;
     seriesType?: EchartsTimeseriesSeriesType;
     stack?: StackType;
+    stackIdSuffix?: string;
     yAxisIndex?: number;
     showValue?: boolean;
     onlyTotal?: boolean;
@@ -179,6 +180,7 @@ export function transformSeries(
     areaOpacity = 1,
     seriesType,
     stack,
+    stackIdSuffix,
     yAxisIndex = 0,
     showValue,
     onlyTotal,
@@ -225,6 +227,9 @@ export function transformSeries(
   } else if (stack && isTrend) {
     stackId = getTimeCompareStackId(forecastSeries.type, timeCompare, name);
   }
+  if (stackId && stackIdSuffix) {
+    stackId += stackIdSuffix;
+  }
   let plotType;
   if (
     !isConfidenceBand &&