Insurgency Sandstorm EasyAntiCheat give Unknon Error #1 after updating to SteamOS 3.6.19 Stable

[positiveoctopus]

Your system information

• Steam client version: 1726693985
• SteamOS version: 3.6.19
• Opted into Steam client beta?: [No]
• Opted into SteamOS beta?: [No]
• Have you checked for updates in Settings > System?: [Yes/]

Please describe your issue in as much detail as possible:

Describe what you expected should happen and what did happen.

Games with EasyAntiCheat give Unknown Error #1 when booting up, making them unplayable after the update, works fine if i revert to SteamOS 3.5

Steps for reproducing this issue:

1. Open a game with EasyAntiCheat, in my case the game is Insurgency Sandstorm which is listed playable on SteamOS
2. Wait for the EasyAntiCheat Client to load to 100%
3. It gives an error and you can only exit the game

[kisak-valve]

Hello @positiveoctopus, we're tracking issues with games run with Proton in the Proton issue tracker. Also, we're using one issue report per unofficially supported game title, so I've gone ahead and transferred this issue report to ValveSoftware/Proton#1651 (comment).