• Streaming device: Original physical Steam Link, Model 1003, hardware ID FL54901AAB
  
• Steam Link firmware: 930
  
• Host: New Steam Machine
  
• SteamOS: 3.8.28, Build 20260922.1
  
• Steam version: 1791918624
  
• Keyboard: QwertyKeys Neo80 Tri-mode
  
• Mouse: Corsair KATAR ELITE WIRELESS
  
• Streaming mode: Balanced
  
• Input Streaming: Enabled
  
• Network: Steam Link connected by Ethernet through a powerline adapter, negotiated at 100 Mbps; Steam Machine connected over 5 GHz Wi-Fi

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When the Neo80 is connected to the Steam Link by USB, it works in the Link interface, but its key presses do not reach the Steam Machine once streaming starts. This happens in games and outside games.

The keyboard works when connected directly to the Steam Machine over USB or Bluetooth. Its 2.4 GHz receiver, when connected to the Steam Link, successfully forwards keyboard input both in the Link interface and during streaming. Connecting the receiver directly to the Steam Machine also works.

I updated the Neo80 tri-mode firmware using QMK Toolbox Beta, but the wired-USB issue remains. Restarting the Steam Link and trying different USB ports did not help.

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Mouse movement and ordinary buttons work while streaming, but both side buttons (Mouse 4/5) produce no input on the Steam Machine. This happens outside games as well as in games.

The Corsair mouse was tested connected to the Steam Link by both USB and its 2.4 GHz receiver, with the same result. Connected directly to the Steam Machine by USB or receiver, it works. Bluetooth connections for both keyboard and mouse also work directly on the host, but are impractical because of the distance.

I do not know whether the mouse side buttons are expected to work in the Steam Link's own interface.

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• The original Steam Controller works when connected to either the Steam Link or the Steam Machine.
  
• Changing USB ports and fully restarting the Link did not resolve either issue.
  
• Balanced streaming mode does not appear to affect these input problems.
  
• I don't have another mouse or keyboard available for comparison.

Is there anything else I could check that would help identify the cause of these problems?

Thank you for any help.