Consider
https://github.com/dotnet/runtime/blob/978df67ced885aeca5f7e75379451bc1a57cc219/src/libraries/System.Net.WebSockets/tests/WebSocketCreateTest.cs#L40-L45

        [OuterLoop("Uses external servers")]
        [Theory]
        [MemberData(nameof(EchoServers))]
        [SkipOnPlatform(TestPlatforms.Browser, "System.Net.Sockets is not supported on this platform.")]
        [ActiveIssue("https://github.com/dotnet/runtime/issues/34690", TestPlatforms.Windows, TargetFrameworkMonikers.Netcoreapp, TestRuntimes.Mono)]
        public async Task WebSocketProtocol_CreateFromConnectedStream_CanSendReceiveData(Uri echoUri)

This has both OuterLoop, and SkipOnPlatform attributes. This should run when using category=outerloop, but get skipped if it is running on the browser. Instead, the tests run anyway, and fail because the operations are not supported on browser.

I can reproduce this with ./dotnet.sh build /bl src/libraries/System.Net.WebSockets/tests/System.Net.WebSockets.Tests.csproj /p:Configuration=Release /p:TargetOS=Browser /p:TargetArchitecture=wasm /t:Test -p:Scenario=WasmTestOnBrowser -p:TestScope=outerloop -p:XUnitClassName=System.Net.WebSockets.Tests.WebSocketTests

this is the xharness command line:
wasm test-browser --app=. --output-directory=/workspaces/runtime/artifacts/bin/System.Net.WebSockets.Tests/Release/net7.0/browser-wasm/AppBundle/xharness-output --browser-arg=--no-sandbox -s dotnet.js.symbols --symbol-patterns wasm-symbol-patterns.txt --browser-arg=--no-sandbox -- --run WasmTestRunner.dll System.Net.WebSockets.Tests.dll -class System.Net.WebSockets.Tests.WebSocketTests -trait category=OuterLoop -notrait category=failing.

I don't think this is wasm, or SkipOnPlatform specific.

cc @akoeplinger @premun