diff --git a/eform-client/playwright/e2e/Page objects/BackendConfigurationCalendar.page.ts b/eform-client/playwright/e2e/Page objects/BackendConfigurationCalendar.page.ts
new file mode 100644
index 0000000000..3778a1a6ec
--- /dev/null
+++ b/eform-client/playwright/e2e/Page objects/BackendConfigurationCalendar.page.ts	
@@ -0,0 +1,118 @@
+import BasePage from './Page';
+import { Page, Locator } from '@playwright/test';
+
+const HOUR_HEIGHT = 52; // px per hour, mirrors calendar-task-block.component.ts
+
+/**
+ * Page object for the backend-configuration calendar
+ * (/plugins/backend-configuration-pn/calendar).
+ *
+ * Encapsulates the create/edit-event flows used by the
+ * "edit must not make the event disappear" regression spec.
+ */
+export class BackendConfigurationCalendarPage extends BasePage {
+  constructor(page: Page) {
+    super(page);
+  }
+
+  async goto() {
+    await this.open('/plugins/backend-configuration-pn/calendar');
+    await this.dayColumns().first().waitFor({ state: 'visible', timeout: 60000 });
+  }
+
+  /** Clickable day cells in the week grid (#cal-day-0 .. #cal-day-6). */
+  dayColumns(): Locator {
+    return this.page.locator('.day-cell-content');
+  }
+
+  /** All rendered event tiles in the week grid. */
+  eventTiles(): Locator {
+    return this.page.locator('.task-content');
+  }
+
+  eventByTitle(title: string): Locator {
+    return this.eventTiles().filter({ hasText: title });
+  }
+
+  /**
+   * Click an empty slot in the given day column (0=Mon .. 6=Sun) at the given
+   * hour to open the create-event modal. Avoids the left edge so the cdk drop
+   * list / task tiles aren't hit.
+   */
+  async openCreateModalOnDay(dayIndex: number, hour: number) {
+    const column = this.page.locator(`#cal-day-${dayIndex}`);
+    await column.waitFor({ state: 'visible', timeout: 40000 });
+    // relY in onCellClick is measured from the cell's own top (no header
+    // offset), so the y position maps directly to the hour.
+    const y = hour * HOUR_HEIGHT;
+    await column.click({ position: { x: 24, y } });
+    await this.page.locator('#calendarEventTitle').waitFor({ state: 'visible', timeout: 20000 });
+  }
+
+  /** Open the first available option of an mtx-select (wraps ng-select). */
+  private async pickFirstOption(triggerSelector: string) {
+    await this.page.locator(triggerSelector).click();
+    const firstOption = this.page.locator('ng-dropdown-panel .ng-option').first();
+    await firstOption.waitFor({ state: 'visible', timeout: 20000 });
+    await firstOption.click();
+  }
+
+  /** Select the repeat option whose label contains the given text (e.g. "Ugentlig"). */
+  private async pickRepeatContaining(text: string) {
+    await this.page.locator('#calendarEventRepeat').click();
+    const option = this.page.locator('ng-dropdown-panel .ng-option').filter({ hasText: text }).first();
+    await option.waitFor({ state: 'visible', timeout: 20000 });
+    await option.click();
+  }
+
+  /**
+   * Create a weekly-recurring event on the given day. This is the exact shape
+   * that triggered the disappear bug: a weekly task whose start lands on a
+   * (trailing-Sunday) day, persisted with a multi-day weekday CSV.
+   */
+  async createWeeklyEvent(dayIndex: number, hour: number, title: string, repeatLabel: string) {
+    await this.openCreateModalOnDay(dayIndex, hour);
+    await this.page.locator('#calendarEventTitle').fill(title);
+    await this.pickRepeatContaining(repeatLabel);
+    // At least one worker must be assigned or the backend rejects the create.
+    await this.pickFirstOption('#calendarEventAssignee');
+    // A report headline (itemPlanningTag) is also required on create.
+    await this.pickFirstOption('#calendarEventPlanningTag');
+    await this.save();
+  }
+
+  /** Open an event's preview popover and click its edit (pencil) button. */
+  async openEditForEvent(title: string) {
+    await this.eventByTitle(title).first().click();
+    const editBtn = this.page.locator('#calendarEventEditBtn');
+    await editBtn.waitFor({ state: 'visible', timeout: 20000 });
+    await editBtn.click();
+    await this.page.locator('#calendarEventTitle').waitFor({ state: 'visible', timeout: 20000 });
+  }
+
+  async setTitle(title: string) {
+    await this.page.locator('#calendarEventTitle').fill(title);
+  }
+
+  /**
+   * Click Save and confirm the recurring-scope dialog if it appears (defaults
+   * to the pre-selected scope — "Only this").
+   */
+  async save() {
+    await this.page.locator('#calendarEventSaveBtn').click();
+    // A recurring series shows a scope dialog first. Target it by id so the
+    // assertion is locale-independent (the visible label is translated).
+    const confirm = this.page.locator('#repeatScopeConfirmBtn');
+    try {
+      await confirm.waitFor({ state: 'visible', timeout: 2500 });
+      await confirm.click();
+    } catch {
+      // No scope dialog — event was not part of a recurring series, or the
+      // save went straight through.
+    }
+    // Wait for the modal to close (save succeeded + week reloaded) rather than
+    // sleeping a fixed amount, so the test isn't flaky under CI load.
+    await this.page.locator('#calendarEventSaveBtn').waitFor({ state: 'hidden', timeout: 20000 });
+    await this.dayColumns().first().waitFor({ state: 'visible', timeout: 20000 });
+  }
+}
diff --git a/eform-client/playwright/e2e/Tests/backend-configuration-calendar/calendar.edit-event-stays-visible.spec.ts b/eform-client/playwright/e2e/Tests/backend-configuration-calendar/calendar.edit-event-stays-visible.spec.ts
new file mode 100644
index 0000000000..14fc7fda14
--- /dev/null
+++ b/eform-client/playwright/e2e/Tests/backend-configuration-calendar/calendar.edit-event-stays-visible.spec.ts
@@ -0,0 +1,66 @@
+import { test, expect } from '@playwright/test';
+import { LoginPage } from '../../Page objects/Login.page';
+import { BackendConfigurationCalendarPage } from '../../Page objects/BackendConfigurationCalendar.page';
+
+/**
+ * Regression guard for the critical bug where editing ANY calendar event made
+ * it disappear from the week view.
+ *
+ * Root cause: a weekly task whose StartDate landed on the trailing Sunday of a
+ * Mon-Sun week was dropped by GetOccurrencesInWeek (Sunday-aligned bucket math
+ * computed weeksFromAnchor = -1). Editing an event moved its StartDate onto the
+ * clicked occurrence's date, so any edit of a Sunday occurrence triggered it.
+ *
+ * This spec reproduces the exact shape end-to-end: a weekly event on Sunday
+ * (which pre-fix would not even render in its own week) is created, then edited,
+ * asserting it stays visible both times.
+ *
+ * Idempotency: a stable title is used and the event is only created when
+ * missing, so reruns reuse the same event instead of accumulating tiles (which
+ * would otherwise occupy the create slot and break click-to-create).
+ */
+test.describe('Backend configuration calendar - edit keeps event visible', () => {
+  let page;
+  let loginPage: LoginPage;
+  let calendar: BackendConfigurationCalendarPage;
+
+  const SUNDAY = 6; // 0=Mon .. 6=Sun
+  const CREATE_HOUR = 3; // empty early-morning slot
+  // BASE is a substring of EDITED, so eventByTitle(BASE) matches the tile in
+  // both states — keeping create-if-missing and the assertions rerun-safe.
+  const BASE = 'PW Regression Weekly Sunday';
+  const EDITED = `${BASE} edited`;
+
+  test.beforeAll(async ({ browser }) => {
+    page = await browser.newPage();
+    loginPage = new LoginPage(page);
+    calendar = new BackendConfigurationCalendarPage(page);
+    await loginPage.open('/');
+    await loginPage.login();
+    await calendar.goto();
+
+    if ((await calendar.eventByTitle(BASE).count()) === 0) {
+      await calendar.createWeeklyEvent(SUNDAY, CREATE_HOUR, BASE, 'Ugentlig');
+    }
+  });
+
+  test.afterAll(async () => {
+    await page.close();
+  });
+
+  test('a weekly Sunday event renders in its own week', async () => {
+    // Pre-fix this failed: a weekly-Sunday event generated no occurrences in
+    // its own week.
+    await expect(calendar.eventByTitle(BASE).first()).toBeVisible({ timeout: 20000 });
+  });
+
+  test('editing the event does not make it disappear', async () => {
+    await calendar.openEditForEvent(BASE);
+    await calendar.setTitle(EDITED);
+    await calendar.save();
+
+    // The exact regression: after a successful edit the event must still be
+    // present in the week grid (pre-fix it vanished).
+    await expect(calendar.eventByTitle(EDITED).first()).toBeVisible({ timeout: 20000 });
+  });
+});