The Arma 3 Launcher (1.5.154.89) crashes every time the mouse moves over a button in the left-hand navigation menu. It finishes loading normally, then closes with an unhandled exception as soon as the pointer enters the menu. The game runs fine when started directly with arma3_x64.exe.

Exception (same in every crash):
System.NullReferenceException: Object reference not set to an instance of an object.
at Launcher.MainWindow.AnimateMainNavigationSliders(Object sender)
at Launcher.MainWindow.ButtonOnMouseEnter(Object sender, MouseEventArgs mouseEventArgs)

Steps to reproduce:

1. Install all Arma 3 DLC, including all creator DLC.

2. Start the launcher from Steam and wait for it to finish loading.

3. Move the mouse over any button in the left-hand menu.

4. The launcher crashes.

It started on the first launcher start after installing all creator DLC on 12 Oct 2026. The launcher had also updated to 1.5.154.89 on 5 Oct and hadn't been started in between, so either could be the trigger.

It still crashes after a launcher cache reset, -safemode, WPF software rendering, a DPI override, Steam file verification, and a full uninstall/purge and clean reinstall with no mods enabled.

Windows 11 Pro 26200, .NET 4.8.1, RTX 4070 Ti (driver 32.0.16.1742), two 1080p monitors at 100% scaling.

Full details, the complete stack trace and everything tried are in the attached "Arma 3 launcher bug report.txt".