DisplayLink monitor detected but never activates — path stays inactive, Windows repor

[biolau]

DisplayLink monitor detected but never activates — path stays inactive, Windows reports success (25H2 build 26200.9445)

My ASUS MB169B+ (DisplayLink, USB-only portable monitor) stopped working on the day
Windows cumulative KB5124008 installed. The device is detected perfectly — it's just
never lit up. DisplayLink Manager sees it and lists it by name, but shows it as
**Disconnected**.

Setup
- Windows 11 25H2, build 26200.9445 (KB5124008, 2026-09-09)
- ASUS MB169B+ (DL-3xxx), USB\VID_17E9&PID_FF0B
- Plugged directly into a USB 3.0 root hub, no dock or hub in between
- Primary display is a 4K screen on an RTX 5090, working fine

What works
- Device enumerates, both interfaces `Status OK`, `ProblemCode 0`
- EDID reads correctly — Windows shows the monitor node as `MB169B+`
- Monitor node's parent is correctly the DisplayLink USB device
- DisplayLink adapter has its own adapter LUID, separate from the GPU
- DisplayLink Manager lists the panel by name

What doesn't
The display path exists and reports available, but never activates:
tgtId=4352 LUID=0:71917 flags=0x1 ACTIVE (primary)
tgtId=256 LUID=0:33781228 flags=0x0 INACTIVE (MB169B+, targetAvailable=1)


Every activation method returns **success** and the path stays at `flags=0x0`:
- `SetDisplayConfig` with an explicitly supplied active path → `rc=0`
- `SetDisplayConfig` with `SDC_TOPOLOGY_EXTEND` → `rc=0`
- `DisplaySwitch.exe /extend` (Win+P → Extend) → no change

Nothing is logged.
No errors in System or Application from the graphics stack
during any attempt. Completely silent failure.

Tried and ruled out
- Two USB ports on two different controllers
- DisplayLink 12.2 M2 *and* 11.5 M3 (the version that was working before) — identical failure
- Clean uninstall/reinstall of both, driver + Manager
- USB selective suspend (already disabled on AC)
- Display topology rebuilt explicitly via the CCD API
- DL-3xxx is still listed as supported in the 12.x release notes
- 25H2 itself — I've been on it since Oct 2025, 11 months before this broke

Can't roll back the update
KB5124008 is a combined SSU+LCU package:
`0x800f0926 — "Permanent package cannot be uninstalled due to container dependency."`
System Restore also fails at `0x80071ab0` on Windows Containers layer files (wcifs),
from WinRE too. So I can't test whether the update is actually the cause.

The one variable I can't change:
DisplayLink Manager is Store-only at 3.2.14.0,
and no older builds are published. The driver has been swung across two major
versions with zero effect, so the driver isn't it — but the Manager has been constant
throughout, and I have no way to vary it.

Questions
1. Anyone else lose a DisplayLink display after KB5124008 / build 26200.9445?
2. Is there any way to get an older DisplayLink Manager build?
3. Does `targetAvailable=1` + `SetDisplayConfig` returning success without activating
ring a bell to anyone? That combination feels like the user-mode host failing to
bring up its swapchain.