From 91bccb3d3d50385b0af06be21a2da30e842da4a9 Mon Sep 17 00:00:00 2001
From: Arkan Ahmedov <arkanahmedov02@gmail.com>
Date: Fri, 24 Jul 2026 11:23:46 +0300
Subject: [PATCH 1/2] fix(grid): ensure final settle position in momentum
 scroll with trailing option

---
 .../igniteui-angular/grids/grid/src/grid-base.directive.ts | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/projects/igniteui-angular/grids/grid/src/grid-base.directive.ts b/projects/igniteui-angular/grids/grid/src/grid-base.directive.ts
index 04af42f9e8d..456f2214e8b 100644
--- a/projects/igniteui-angular/grids/grid/src/grid-base.directive.ts
+++ b/projects/igniteui-angular/grids/grid/src/grid-base.directive.ts
@@ -3698,7 +3698,12 @@ export abstract class IgxGridBaseDirective implements GridType,
                 this.throttleTime$.pipe(
                     take(1),
                     switchMap(time => timer(time, this.throttleScheduler))
-                )
+                ),
+                // `trailing: true` ensures the final settle position of a fast momentum
+                // scroll is processed; otherwise the last scroll events are dropped and the
+                // rows stay frozen at an intermediate startIndex while the scrollbar is at top.
+                // `leading: true` keeps the immediate response on scroll start.
+                { leading: true, trailing: true }
             ),
             destructor
         )

From 592caaad8793bdad4b549bc0dbfda671738331ae Mon Sep 17 00:00:00 2001
From: Arkan Ahmedov <arkanahmedov02@gmail.com>
Date: Fri, 24 Jul 2026 11:24:00 +0300
Subject: [PATCH 2/2] test(grid): add regression coverage for momentum-scroll
 trailing settle

Drives the vertical scrollNotify stream with an intermediate (leading-edge)
position followed by a scrollTop=0 settle in the same throttle window, so the
settle can only be delivered on the trailing edge. Asserts the grid resets to
startIndex 0 / renders row 0, guarding against the dropped-trailing throttle
config that left the top rows frozen out of view.
---
 .../grids/grid/src/grid.component.spec.ts     | 32 +++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/projects/igniteui-angular/grids/grid/src/grid.component.spec.ts b/projects/igniteui-angular/grids/grid/src/grid.component.spec.ts
index f8ce0013662..33381e3ac72 100644
--- a/projects/igniteui-angular/grids/grid/src/grid.component.spec.ts
+++ b/projects/igniteui-angular/grids/grid/src/grid.component.spec.ts
@@ -2161,6 +2161,38 @@ describe('IgxGrid Component Tests #grid', () => {
 
                 expect(grid.headerContainer.state.startIndex).toBeGreaterThan(0);
             });
+
+            it('should settle at the top row when a fast momentum scroll ends at scrollTop 0 (throttle trailing edge)', async () => {
+                const fix = TestBed.createComponent(ZonelessTallGridComponent);
+                fix.detectChanges();
+                await fix.whenStable();
+                const grid = fix.componentInstance.grid;
+                const virtDir = grid.verticalScrollContainer;
+                const scrollEl = virtDir.getScroll();
+                const maxScroll = scrollEl.scrollHeight - scrollEl.clientHeight;
+
+                // Move away from the top so the first rows are virtualized out of view.
+                grid.scrollNotify.next({ target: { scrollTop: maxScroll } });
+                await wait(50);
+                await fix.whenStable();
+                expect(virtDir.state.startIndex).toBeGreaterThan(0);
+
+                // Simulate a fast momentum/inertia scroll back to the top: an intermediate
+                // position lands on the throttle's leading edge and the scrollTop = 0 settle
+                // arrives within the same throttle window, so it can only be delivered on the
+                // trailing edge. Feeding scrollNotify directly (instead of setting scrollTop)
+                // avoids the browser's async native scroll events - which all read the final
+                // scrollTop of 0 - from masking a dropped-trailing regression.
+                grid.scrollNotify.next({ target: { scrollTop: Math.round(maxScroll / 2) } });
+                grid.scrollNotify.next({ target: { scrollTop: 0 } });
+                await wait(50);
+                await fix.whenStable();
+
+                // Without the trailing edge the settle event is dropped and the grid stays
+                // frozen at an intermediate startIndex while the scrollbar sits at the top.
+                expect(virtDir.state.startIndex).toBe(0);
+                expect(grid.gridAPI.get_row_by_index(0)).toBeDefined();
+            });
         });
     });