Object reference not set to an instance of an object when close with two cefsharp.winforms instances - cefsharp

Question

My wpf uses two ChromiumWebBrowser(Cefsharp.Winforms) instances, one is for my website, one is for displaying pdf file, when I close the MianWindow, there is a crash like below:
System.NullReferenceException
HResult=0x80004003
Message=Object reference not set to an instance of an object.
Source=CefSharp.WinForms
StackTrace:
在 CefSharp.WinForms.ChromiumWebBrowser.InternalDispose(Boolean disposing)
在 CefSharp.WinForms.ChromiumWebBrowser.Dispose(Boolean disposing)
在 System.ComponentModel.Component.Dispose()
在 System.Windows.Forms.Control.Dispose(Boolean disposing)
在 System.Windows.Forms.Integration.WinFormsAdapter.Dispose(Boolean disposing)
在 System.ComponentModel.Component.Dispose()
在 System.Windows.Forms.Integration.WindowsFormsHost.Dispose(Boolean disposing)
在 System.Windows.Interop.HwndHost.WeakEventDispatcherShutdown.OnShutdownFinished(Object sender, EventArgs e)
在 System.EventHandler.Invoke(Object sender, EventArgs e)
在 System.Windows.Threading.Dispatcher.ShutdownImplInSecurityContext(Object state)
在 System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
在 System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
在 System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
在 MS.Internal.CulturePreservingExecutionContext.Run(CulturePreservingExecutionContext executionContext, ContextCallback callback, Object state)
在 System.Windows.Threading.Dispatcher.ShutdownImpl()
在 System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
在 System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame)
在 System.Windows.Application.RunDispatcher(Object ignore)
在 System.Windows.Application.RunInternal(Window window)
在 System.Windows.Application.Run(Window window)
在 System.Windows.Application.Run()
I didn't set CefSharpSettings.ShutdownOnExit explicitly, in my close function, just call:
Application.Current.Shutdown();
It is ok if remove one for pdf.
I host the browser in like below:
<WindowsFormsHost Name="browserHost">
<cefwpf:ChromiumWebBrowser x:Name="browser" IsBrowserInitializedChanged="browser_IsBrowserInitializedChanged">
</cefwpf:ChromiumWebBrowser>
</WindowsFormsHost>
My cefsharp version is 83.1.100
Thanks for any help!