Windows 11 - Sunshine Immediately Crashes After Opening The Localhost Web UI

[9wow]

Is there an existing issue for this?

• I have searched the existing issues

Is your issue described in the documentation?

• I have read the documentation

Is your issue present in the latest beta/pre-release?

None

Describe the Bug

After launching Sunshine it stalls on 'Waiting for Web UI to be ready............................................' and when the localhost web-ui is opened in my browser, the tab says 'Unable to connect' - 'Firefox can’t establish a connection to the server at localhost:xxxx'.

Expected Behavior

1. The web-ui should open and request my login after the Terminal closes.
2. The Sunshine icon should be in the systray and have a running process in Task Manager.

Additional Context

I just updated to the latest Sunshine in an attempt to solve this, but no luck. Most probably something to do with this Windows version as Sunshine was working perfectly fine before 24H2 26100.6899

Host Operating System

Windows

Operating System Version

Windows 11 Pro 24H2 26100.6899

Architecture

amd64/x86_64

Sunshine commit or version

2025.924.154138 commit: 86188d4

Package

Windows - installer (recommended)

GPU Type

NVIDIA

GPU Model

RTX 5090

GPU Driver/Mesa Version

NVIDIA Studio Driver 581.57

Capture Method

None

Config

lan_encryption_mode = 2
native_pen_touch = disabled
nvenc_latency_over_power = disabled
nvenc_realtime_hags = disabled
sw_tune = stillimage
wan_encryption_mode = 2

Apps

Relevant log output

[2025-10-27 07:29:16.197]: Info: Sunshine version: v2025.628.4510
[2025-10-27 07:29:16.197]: Info: Package Publisher: LizardByte
[2025-10-27 07:29:16.197]: Info: Publisher Website: https://app.lizardbyte.dev
[2025-10-27 07:29:16.197]: Info: Get support: https://app.lizardbyte.dev/support
[2025-10-27 07:29:16.197]: Info: config: 'lan_encryption_mode' = 2
[2025-10-27 07:29:16.197]: Info: config: 'native_pen_touch' = disabled
[2025-10-27 07:29:16.197]: Info: config: 'nvenc_latency_over_power' = disabled
[2025-10-27 07:29:16.197]: Info: config: 'nvenc_realtime_hags' = disabled
[2025-10-27 07:29:16.197]: Info: config: 'sw_tune' = stillimage
[2025-10-27 07:29:16.197]: Info: config: 'wan_encryption_mode' = 2

[Yundi339]

https://learn.microsoft.com/en-us/answers/questions/5585563/localhost-not-working-anymore-after-2025-10-cumula
The October 2025 Cumulative Update (KB5066835) has introduced a regression affecting certain HTTP/2 and loopback traffic scenarios.