It looks like WebSphere is trying to process an HTTP Upgrade request but fails because the upgrade mechanism isn't properly implemented or configured. This error usually happens when WebSockets or another protocol upgrade is attempted without proper support in WebSphere.

Possible Causes & Fixes:

1. Check WebSphere’s Support for HTTP Upgrades

WebSphere 9.0.5.6 might not fully support HTTP upgrades for certain protocols. If your application uses WebSockets or HTTP/2, ensure WebSphere is configured correctly.

2. Verify WebSphere Settings

In the WebSphere Admin Console, navigate to Server > Web Container Settings and check if HTTP Upgrade is enabled.

If you are using WebSockets, make sure WebSocket support is turned on.

3. Check Your Code for Upgrade Requests

If your application explicitly calls request.upgrade(HttpUpgradeHandler.class), make sure the HttpUpgradeHandler implementation is correct and compatible with WebSphere.

4. Enable Detailed Logging for More Clarity

Since enabling com.ibm.ws.webcontainer logging didn’t help, try increasing verbosity with:

*=info:com.ibm.ws.webcontainer.*=all

This may provide more details on why the upgrade is failing.

5. Update WebSphere (If Possible)

WebSphere 9.0.5.6 is a bit old, and IBM may have addressed this issue in later fix packs. Consider updating WebSphere to the latest available version.

6. Workaround: Disable HTTP Upgrade (If Not Needed)

If your application doesn’t actually require HTTP Upgrade, you might be able to modify your request handling logic or configure WebSphere to reject upgrade requests.

Would be great if you could share whether your application is using WebSockets or another upgrade protocol—it might help narrow down the exact issue!