Using Delphi 10.2 (under Windows 10 "19H2"), I can create a new app, drop a single panel on it, and an action list with two items. Both items call the same routine whose purpose is to remove any buttons on the panel, and then add the new ones in:

```
procedure TForm1.CreateNavPanelButtons(Action: TAction);
begin
  NavPanel.RemoveObject(Btn);
  Btn.DisposeOf; //problem line

  Btn := MakeButton(Action);
  NavPanel.AddObject(Btn);
end;

```

(I've simplified to just use one button here.) Remove the existing button, add the new button in. If I call DisposeOf (to free up the button's memory), the Window object becomes unresponsive (can't resize, move, close) until I shift focus away from the app.

I've included the entire code below:

```
unit Unit1;

interface

uses
  System.SysUtils, System.Types, System.UITypes, System.Classes, System.Variants,
  FMX.Types, FMX.Controls, FMX.Forms, FMX.Graphics, FMX.Dialogs, FMX.StdCtrls,
  FMX.Controls.Presentation, System.Actions, FMX.ActnList;

type
  TForm1 = class(TForm)
    NavPanel: TPanel;
    ActionList: TActionList;
    acNextMenu: TAction;
    acBackToMainMenu: TAction;
    procedure FormCreate(Sender: TObject);
    procedure acNextMenuExecute(Sender: TObject);
  private
    { Private declarations }
  public
    Btn: TButton;
    procedure CreateNavPanelButtons(Action: TAction);
  end;

var
  Form1: TForm1;

implementation

{$R *.fmx}

function MakeButton(A: TAction): TButton;
begin
  Result := TButton.Create(nil);
  Result.Action := A;
  Result.Text := (A as TAction).Text;
end;

procedure TForm1.acNextMenuExecute(Sender: TObject);
begin
  CreateNavPanelButtons(acBackToMainMenu);
end;

procedure TForm1.CreateNavPanelButtons(Action: TAction);
begin
  NavPanel.RemoveObject(Btn);
  Btn.DisposeOf;

  Btn := MakeButton(Action);
  NavPanel.AddObject(Btn);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  CreateNavPanelButtons(acNextMenu);
end;

end.

```

Here's the form:

```
object Form1: TForm1
  Left = 0
  Top = 0
  Caption = 'Form1'
  ClientHeight = 480
  ClientWidth = 640
  FormFactor.Width = 320
  FormFactor.Height = 480
  FormFactor.Devices = [Desktop]
  OnCreate = FormCreate
  DesignerMasterStyle = 0
  object NavPanel: TPanel
    Align = Top
    Size.Width = 640.000000000000000000
    Size.Height = 73.000000000000000000
    Size.PlatformDefault = False
    TabOrder = 0
  end
  object ActionList: TActionList
    Left = 392
    Top = 192
    object acNextMenu: TAction
      Category = 'Navigation'
      Text = 'NextMenu'
      OnExecute = acNextMenuExecute
    end
    object acBackToMainMenu: TAction
      Category = 'Navigation'
      Text = 'Back To &Main Menu'
      OnExecute = FormCreate
    end
  end
end

```