UI difference in Composite after migrating eclipse based application from version 4.15 to 4.26

Question

We have migrated our eclipse based application from eclipse 4.15 to eclipse 4.26, and while testing the application we found an UI difference in composite. We have able to see the slant line from bottom right hand side corner. The UI is not rendered properly.

We are able to see for all the Composites which are not selected.

When we click on one of the composite, then these issue is not seen. Seems like coolbar is visible for these and which overrides the slant lines/issue

Also, we are getting null pointer exception

I expected: < No change in UI>

But got: <Change in Composite Rendering, getting slant lines from bottom right side corner>

    [![!ENTRY org.eclipse.e4.ui.workbench 4 0 2025-02-25 11:41:40.629
!MESSAGE An exception occurred while notifying part listeners
!STACK 0
java.lang.NullPointerException: Cannot read field "layout" because "this" is null
    at org.eclipse.swt.widgets.Composite.markLayout(Composite.java:861)
    at org.eclipse.swt.widgets.Composite.layout(Composite.java:824)
    at org.eclipse.swt.widgets.Control.requestLayout(Control.java:2398)
    at org.eclipse.ui.internal.CoolBarToTrimManager.update(CoolBarToTrimManager.java:602)
    at org.eclipse.ui.internal.WorkbenchWindow.updateActionBars(WorkbenchWindow.java:2492)
    at org.eclipse.ui.internal.WorkbenchPage.updateActionBars(WorkbenchPage.java:4334)
    at org.eclipse.ui.internal.WorkbenchPage$ActionSwitcher.updateActivePart(WorkbenchPage.java:668)
    at org.eclipse.ui.internal.WorkbenchPage.updateActivations(WorkbenchPage.java:331)
    at org.eclipse.ui.internal.WorkbenchPage$E4PartListener.partActivated(WorkbenchPage.java:212)
    at org.eclipse.e4.ui.internal.workbench.PartServiceImpl$2.run(PartServiceImpl.java:250)
    at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:45)
    at org.eclipse.e4.ui.internal.workbench.PartServiceImpl.firePartActivated(PartServiceImpl.java:247)
    at org.eclipse.e4.ui.internal.workbench.PartServiceImpl.activate(PartServiceImpl.java:774)
    at org.eclipse.e4.ui.internal.workbench.PartServiceImpl.activate(PartServiceImpl.java:683)
    at org.eclipse.e4.ui.internal.workbench.swt.AbstractPartRenderer.activate(AbstractPartRenderer.java:97)
    at org.eclipse.e4.ui.workbench.renderers.swt.StackRenderer.lambda$3(StackRenderer.java:963)
    at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:89)
    at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4256)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1066)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1090)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1075)
    at org.eclipse.swt.widgets.Shell.setActiveControl(Shell.java:1530)
    at org.eclipse.swt.widgets.Shell.WM_MOUSEACTIVATE(Shell.java:2441)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:4787)
    at org.eclipse.swt.widgets.Canvas.windowProc(Canvas.java:340)
    at org.eclipse.swt.widgets.Decorations.windowProc(Decorations.java:1478)
    at org.eclipse.swt.widgets.Shell.windowProc(Shell.java:2284)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:5022)
    at org.eclipse.swt.internal.win32.OS.DefWindowProc(Native Method)
    at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:91)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:4844)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:5022)
    at org.eclipse.swt.internal.win32.OS.DefWindowProc(Native Method)
    at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:91)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:4844)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:5022)
    at org.eclipse.swt.internal.win32.OS.DefWindowProc(Native Method)
    at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:91)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:4844)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:5022)
    at org.eclipse.swt.internal.win32.OS.DefWindowProc(Native Method)
    at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:91)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:4844)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:5022)
    at org.eclipse.swt.internal.win32.OS.DefWindowProc(Native Method)
    at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:91)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:4844)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:5022)
    at org.eclipse.swt.internal.win32.OS.DefWindowProc(Native Method)
    at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:91)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:4844)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:5022)][1]][1]

In First Photo, third composite is selected, no issue is seen. Issue is seen in first two parts. In Second Photo, second composite is selected, so no issue is seen. Issue is seen in first and last parts.