[Bug] V1 not responding to USB handshake when entering DFU

[slainless]

Describe the Bug

Using changes from upstream QMK, latest branch 2025q3, or vial fork results in firmware not responding to USB handshake, failing to respond to device descriptor request from OS. This happens when in DFU-mode.

The operational of the keyboard remains ok though. Only the DFU part is a bit problematic, essentially breaking DFU-mode after flashing non-"official" firmware.

Keyboard Used

v1/ansi

Link to product page (if applicable)

No response

Operating System

Windows

qmk doctor Output

Ψ Wrote configuration to C:/Users/slainless/AppData/Local/QMK.EXE/qmk.exe/qmk.exe.ini
Ψ QMK Doctor is checking your environment.
Ψ CLI version: 1.1.8
Ψ QMK home: D:/Projects/qmk_firmware
Ψ Detected Windows 11 (10.0.26100).
Ψ Userspace enabled: False
Ψ Git branch: 2025q3
Ψ Repo version: 0.14.29
⚠ Git has unstashed/uncommitted changes.
Ψ - Latest 2025q3: 2025-11-21 14:38:17 +0800 (790841c92d) -- Add Q12 HE ANSI/ISO
Ψ - Latest upstream/master: None
Ψ - Latest upstream/develop: None
Ψ - Common ancestor with upstream/master: None
Ψ - Common ancestor with upstream/develop: None
Ψ All dependencies are installed.
Ψ Found arm-none-eabi-gcc version 13.3.0
Ψ Successfully compiled using arm-none-eabi-gcc
Ψ Successfully tested arm-none-eabi-binutils using arm-none-eabi-size
Ψ Found avr-gcc version 15.1.0
Ψ Successfully compiled using avr-gcc
Ψ Successfully tested avr-binutils using avr-size
Ψ Found avrdude version 8.0-2025011
Ψ Found dfu-programmer version 1.1.0
Ψ Found dfu-util version 0.11
Ψ Submodules are up to date.
Ψ Submodule status:
Ψ - lib/chibios: 2025-10-14 11:51:26 +0800 --  (41e112ce20)
Ψ - lib/chibios-contrib: 2025-09-28 10:35:52 +0800 --  (6e7400ea)
Ψ - lib/googletest: 2021-06-11 06:37:43 -0700 --  (e2239ee6)
Ψ - lib/lufa: 2022-08-26 12:09:55 +1000 --  (549b97320)
Ψ - lib/vusb: 2022-06-13 09:18:17 +1000 --  (819dbc1)
Ψ - lib/printf: 2022-06-29 23:59:58 +0300 --  (c2e3b4e)
Ψ - lib/pico-sdk: 2025-04-20 21:24:29 +1000 --  (d0c5cac)
Ψ - lib/lvgl: 2022-04-11 04:44:53 -0600 --  (e19410f8)
Ψ QMK is ready to go, but minor problems were found

Is AutoHotKey / Karabiner installed

• AutoHotKey (Windows)
• Karabiner (macOS)

Other keyboard-related software installed

No response

Additional Context

No response

[lokher]

The operational of the keyboard remains ok though. with stock firmware or customed firmware?

Did you use "esc" or button underneath space bar to trigger DFU ?

[slainless]

The operational of the keyboard remains ok though. with stock firmware or customed firmware?

Both, custom firmware or stock firmware works fine, i see no difference in daily usage between them. The only problematic point is the DFU-mode of the custom firmware.

Did you use "esc" or button underneath space bar to trigger DFU ?

I have tried either with ESC or reset under space bar. Both result in same behaviour. It seems to enter DFU correctly, but after that, it will never (or fail to) responds to USB communication for the duration of the DFU.