From bc75d48f8fe4af9c262f87ce3ce1be705d89c28b Mon Sep 17 00:00:00 2001
From: Sergio Bur <sjbur.dev@gmail.com>
Date: Thu, 8 Jan 2026 15:50:50 +0100
Subject: [PATCH 1/2] fix: fix bug

---
 .../__internal/scheduler/workspaces/m_work_space.ts | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/packages/devextreme/js/__internal/scheduler/workspaces/m_work_space.ts b/packages/devextreme/js/__internal/scheduler/workspaces/m_work_space.ts
index c1649f57b664..0aaf1cff5b33 100644
--- a/packages/devextreme/js/__internal/scheduler/workspaces/m_work_space.ts
+++ b/packages/devextreme/js/__internal/scheduler/workspaces/m_work_space.ts
@@ -1579,13 +1579,24 @@ class SchedulerWorkSpace extends Widget<WorkspaceOptionsInternal> {
       startIndex = totalCellCount;
     }
 
+    let foundElements = 0;
     for (let i = startIndex; i < totalCellCount + cellCount; i++) {
       const element = $($cells).eq(i).get(0);
       const elementWidth = element ? getBoundingRect(element).width : 0;
       width += elementWidth;
+      if (element) {
+        foundElements++;
+      }
     }
 
-    return width / (totalCellCount + cellCount - startIndex);
+    const divisor = totalCellCount + cellCount - startIndex;
+    let result = width / divisor;
+
+    if (result === 0 && groupIndex > 0 && foundElements === 0) {
+      result = this.getRoundedCellWidth(0, 0, cellCount);
+    }
+
+    return result;
   }
 
   // Mappings

From 29c296c56dd01bdda23f657c71b0e40f198643ef Mon Sep 17 00:00:00 2001
From: Sergio Bur <sjbur.dev@gmail.com>
Date: Thu, 8 Jan 2026 18:47:02 +0100
Subject: [PATCH 2/2] feat: add test

---
 .../scheduler/__tests__/workspace.test.ts     | 71 +++++++++++++++++++
 1 file changed, 71 insertions(+)
 create mode 100644 packages/devextreme/js/__internal/scheduler/__tests__/workspace.test.ts

diff --git a/packages/devextreme/js/__internal/scheduler/__tests__/workspace.test.ts b/packages/devextreme/js/__internal/scheduler/__tests__/workspace.test.ts
new file mode 100644
index 000000000000..2721336bba4f
--- /dev/null
+++ b/packages/devextreme/js/__internal/scheduler/__tests__/workspace.test.ts
@@ -0,0 +1,71 @@
+import {
+  afterEach, beforeEach, describe, expect, it,
+} from '@jest/globals';
+import $ from '@js/core/renderer';
+
+import fx from '../../../common/core/animation/fx';
+import { createScheduler } from './__mock__/create_scheduler';
+import { setupSchedulerTestEnvironment } from './__mock__/m_mock_scheduler';
+
+const CLASSES = {
+  scheduler: 'dx-scheduler',
+  workSpace: 'dx-scheduler-work-space',
+  shaderTop: 'dx-scheduler-date-time-shader-top',
+};
+
+describe('Workspace', () => {
+  beforeEach(() => {
+    fx.off = true;
+    setupSchedulerTestEnvironment({ height: 600 });
+  });
+
+  afterEach(() => {
+    const $scheduler = $(document.querySelector(`.${CLASSES.scheduler}`));
+    // @ts-expect-error
+    $scheduler.dxScheduler('dispose');
+    document.body.innerHTML = '';
+    fx.off = false;
+  });
+
+  it('should use group 0 width as fallback when groups are not rendered due to virtual scrolling (T1310524)', async () => {
+    const resources = [
+      { text: 'Room 1', id: 1, color: '#cb6bb2' },
+      { text: 'Room 2', id: 2, color: '#56ca85' },
+      { text: 'Room 3', id: 3, color: '#1e90ff' },
+      { text: 'Room 4', id: 4, color: '#ff9747' },
+      { text: 'Room 5', id: 5, color: '#ff6a00' },
+      { text: 'Room 6', id: 6, color: '#ffc0cb' },
+    ];
+
+    const { scheduler } = await createScheduler({
+      currentView: 'week',
+      views: ['week'],
+      groups: ['roomId'],
+      resources: [{ fieldExpr: 'roomId', dataSource: resources, label: 'Room' }],
+      dataSource: [
+        {
+          text: 'Meeting 1', startDate: new Date(2025, 9, 15, 9), endDate: new Date(2025, 9, 15, 10), roomId: 1,
+        },
+        {
+          text: 'Meeting 2', startDate: new Date(2025, 9, 15, 9), endDate: new Date(2025, 9, 15, 10), roomId: 4,
+        },
+      ],
+      startDayHour: 8,
+      endDayHour: 18,
+      currentDate: new Date(2025, 9, 15),
+      height: 400,
+      shadeUntilCurrentTime: true,
+      scrolling: { mode: 'virtual' },
+    });
+
+    const workSpace = scheduler.getWorkSpace();
+    const cellCount = workSpace._getCellCount();
+    const lastGroupWidth = workSpace.getRoundedCellWidth(
+      resources.length - 1,
+      (resources.length - 1) * cellCount,
+      cellCount,
+    );
+
+    expect(lastGroupWidth).toBeGreaterThan(0);
+  });
+});