Remote Play performance collapses after ~10 seconds when Legion Go Z2 is connected to external HDMI 2.1 display via USB-C dock (SteamOS stable)

[tuxiano]

System Information

Component	Details
Device	Lenovo Legion Go Z2
Operating System	SteamOS (stable channel)
Gamescope version	Current stable (bundled with SteamOS)
GPU	AMD Radeon 780M (RDNA3 iGPU)
Display connection type	USB-C (DisplayPort 1.4 Alt-Mode → HDMI 2.1 through dock)
Dock	Baseus 6-in-1 USB-C Docking Station (B0CGWM48LS)
HDMI cable	Anker Ultra High Speed HDMI 2.1 Cable (B0BRKCN4XK)
External display	Sony Bravia XR-55X90J (HDMI 4)
Display input used	HDMI 4 (4K 120 Hz, VRR capable)
Steam Client	Stable channel (same version on both host and client)

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Description

When using Steam Remote Play between two SteamOS devices (both on the stable channel), gameplay initially runs smoothly but after about 10 seconds the stream begins to lag heavily and becomes unplayable — only when the Lenovo Legion Go Z2 is connected to an external HDMI 2.1 display via USB-C dock.

• Using the built-in display → works flawlessly
• Using Moonlight + Sunshine → works flawlessly (same display, dock, and cable)
• Using Steam Remote Play + external display → smooth for ~10 s, then severe lag/stutter/frame drops

Audio remains normal while video becomes extremely choppy and delayed.

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Steps to Reproduce

1. Connect the Sony Bravia XR-55X90J to the Legion Go Z2 using the Baseus 6-in-1 USB-C dock (DisplayPort Alt-Mode → HDMI 2.1).
2. Boot into SteamOS (stable).
3. Enter Game Mode and start Steam.
4. Launch a Remote Play session from another SteamOS or desktop Steam client.
5. Play for 10–20 seconds and observe performance degradation.

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Expected Behavior

Remote Play should remain smooth and stable regardless of whether the Legion Go Z2 is using its internal display or an external HDMI display connected via USB-C.

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Actual Behavior

Phase	Behavior
0 – 10 s	Smooth 60–120 FPS gameplay, normal latency
≥ 10 s	Rapid frame-time spikes, severe stutter (~1–3 FPS video), large input delay
Throughout	Audio remains normal; stream stays connected
Disconnect external display	Restart game; works normally

Changing HDMI input mode or display settings has no effect:

Setting	Tried	Result
Resolution	1080p / 1440p / 4K	Same lag
HDR	On / Off	Same lag
VRR	On / Off	Same lag
HDMI input mode (TV)	Standard / 4K Optimized / VRR	Same lag
Moonlight client	✅ Works perfectly	✅

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Analysis / Suspected Cause

• The stream starts fine → initial encoder/decoder and gamescope setup work.
• Performance collapse after ~10 s suggests display-sync or VRR negotiation issues once HDMI output (via DisplayPort Alt-Mode) is active.
• Possibly related to gamescope’s output-selection or frame-pacing bugs when external connectors are used:
  • ublue-os/bazzite #1309
  • ValveSoftware/gamescope #1596
• External display works perfectly in Desktop Mode — issue only occurs in Game Mode (gamescope).