diff --git a/src/processor/dataStack.ts b/src/processor/dataStack.ts
index ab41b864d8..eb167cb965 100644
--- a/src/processor/dataStack.ts
+++ b/src/processor/dataStack.ts
@@ -150,7 +150,11 @@ function calculateStack(stackInfoList: StackInfo[]) {
 
                     // Considering positive stack, negative stack and empty data
                     if (
-                        stackStrategy === 'all' // single stack group
+                        // A null/NaN value in a lower series must be excluded from the
+                        // stack, otherwise it corrupts the sum. The other strategies
+                        // already reject it via their `val > 0`/`val < 0` checks, but
+                        // `all` needs an explicit guard. See #21685.
+                        (stackStrategy === 'all' && !isNaN(val)) // single stack group
                         || (stackStrategy === 'positive' && val > 0)
                         || (stackStrategy === 'negative' && val < 0)
                         || (stackStrategy === 'samesign' && sum >= 0 && val > 0) // All positive stack
diff --git a/test/ut/spec/data/dataStack.test.ts b/test/ut/spec/data/dataStack.test.ts
new file mode 100644
index 0000000000..42e230c665
--- /dev/null
+++ b/test/ut/spec/data/dataStack.test.ts
@@ -0,0 +1,71 @@
+/*
+* Licensed to the Apache Software Foundation (ASF) under one
+* or more contributor license agreements.  See the NOTICE file
+* distributed with this work for additional information
+* regarding copyright ownership.  The ASF licenses this file
+* to you under the Apache License, Version 2.0 (the
+* "License"); you may not use this file except in compliance
+* with the License.  You may obtain a copy of the License at
+*
+*   http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing,
+* software distributed under the License is distributed on an
+* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+* KIND, either express or implied.  See the License for the
+* specific language governing permissions and limitations
+* under the License.
+*/
+
+import { createChart, getECModel } from '../../core/utHelper';
+import { EChartsType } from '../../../../src/echarts';
+
+describe('processor/dataStack', function () {
+
+    let chart: EChartsType;
+    beforeEach(function () {
+        chart = createChart();
+    });
+
+    afterEach(function () {
+        chart.dispose();
+    });
+
+    function getStackResult(seriesIndex: number, dataIndex: number): number {
+        const data = getECModel(chart).getSeriesByIndex(seriesIndex).getData();
+        const stackResultDim = data.getCalculationInfo('stackResultDimension');
+        return data.get(stackResultDim, dataIndex) as number;
+    }
+
+    // Regression test for #21685: with `stackStrategy: 'all'`, a null/'-' value
+    // in a lower series used to corrupt the stacked sum (NaN), making the upper
+    // series' bar disappear. The null should be excluded from the stack instead.
+    it('excludes null values from the stack when stackStrategy is "all" (#21685)', function () {
+        chart.setOption({
+            xAxis: { type: 'category', data: ['A', 'B', 'C'] },
+            yAxis: { type: 'value' },
+            series: [
+                {
+                    type: 'bar',
+                    stack: 'total',
+                    data: [10, null, 30]
+                },
+                {
+                    type: 'bar',
+                    stack: 'total',
+                    stackStrategy: 'all',
+                    data: [5, 5, 5]
+                }
+            ]
+        });
+
+        // Index 0 and 2: the lower series has valid values, so they stack normally.
+        expect(getStackResult(1, 0)).toBe(15);
+        expect(getStackResult(1, 2)).toBe(35);
+
+        // Index 1: the lower series is null. It must be excluded from the stack,
+        // so the upper series keeps its own value instead of becoming NaN.
+        expect(getStackResult(1, 1)).toBe(5);
+    });
+
+});