diff --git a/.editorconfig b/.editorconfig
index 2bbdd48250..0aff6e75ca 100644
--- a/.editorconfig
+++ b/.editorconfig
@@ -8,6 +8,12 @@ insert_final_newline = true
 indent_style = space
 indent_size = 4
 
+dotnet_diagnostic.VSTHRD002.severity = none
+dotnet_diagnostic.VSTHRD003.severity = none
+dotnet_diagnostic.VSTHRD105.severity = none
+dotnet_diagnostic.VSTHRD110.severity = none
+dotnet_diagnostic.VSTHRD200.severity = none
+
 [*.cs]
 indent_size = 4
 
diff --git a/build/Packages.props b/build/Packages.props
index 3046dae4dc..88cec7fc18 100644
--- a/build/Packages.props
+++ b/build/Packages.props
@@ -62,8 +62,8 @@
     <PackageReference Update="NuGet.ProjectModel" Version="$(NuGetPackageVersion)" />
     <PackageReference Update="NuGet.Versioning" Version="$(NuGetPackageVersion)" />
 
-    <PackageReference Update="OmniSharp.Extensions.LanguageServer" Version="0.18.0-beta0081" />
-    <PackageReference Update="OmniSharp.Extensions.LanguageProtocol.Testing" Version="0.18.0-beta0081" />
+    <PackageReference Update="OmniSharp.Extensions.LanguageServer" Version="0.18.3" />
+    <PackageReference Update="OmniSharp.Extensions.LanguageProtocol.Testing" Version="0.18.3" />
 
     <PackageReference Update="SQLitePCLRaw.bundle_green" Version="1.1.2" />
     <PackageReference Update="System.Collections.Immutable" Version="1.4.0" />
diff --git a/src/OmniSharp.Host/MSBuild/Discovery/MSBuildLocator.cs b/src/OmniSharp.Host/MSBuild/Discovery/MSBuildLocator.cs
index 872a17758d..24c2435a2c 100644
--- a/src/OmniSharp.Host/MSBuild/Discovery/MSBuildLocator.cs
+++ b/src/OmniSharp.Host/MSBuild/Discovery/MSBuildLocator.cs
@@ -36,7 +36,11 @@ protected override void DisposeCore(bool disposing)
         {
             if (RegisteredInstance != null)
             {
-                AppDomain.CurrentDomain.AssemblyResolve -= Resolve;
+                try
+                {
+                    AppDomain.CurrentDomain.AssemblyResolve -= Resolve;
+                }
+                catch (AppDomainUnloadedException){ } // Ignore if the AppDomain is going away (like during a test in xunit)
                 RegisteredInstance = null;
             }
         }
diff --git a/src/OmniSharp.LanguageServerProtocol/Handlers/OmniSharpCodeActionHandler.cs b/src/OmniSharp.LanguageServerProtocol/Handlers/OmniSharpCodeActionHandler.cs
index 793c32aa61..bfe2dc049a 100644
--- a/src/OmniSharp.LanguageServerProtocol/Handlers/OmniSharpCodeActionHandler.cs
+++ b/src/OmniSharp.LanguageServerProtocol/Handlers/OmniSharpCodeActionHandler.cs
@@ -19,7 +19,7 @@
 
 namespace OmniSharp.LanguageServerProtocol.Handlers
 {
-    internal sealed class OmniSharpCodeActionHandler : CodeActionHandler, IExecuteCommandHandler
+    internal sealed class OmniSharpCodeActionHandler : CodeActionHandlerBase, IExecuteCommandHandler
     {
         public static IEnumerable<IJsonRpcHandler> Enumerate(
             RequestHandlers handlers,
@@ -116,6 +116,11 @@ public override async Task<CommandOrCodeActionContainer> Handle(CodeActionParams
                 codeActions.Select(ca => new CommandOrCodeAction(ca)));
         }
 
+        public override Task<CodeAction> Handle(CodeAction request, CancellationToken cancellationToken)
+        {
+            return Task.FromResult(request);
+        }
+
         public async Task<Unit> Handle(ExecuteCommandParams request, CancellationToken cancellationToken)
         {
             Debug.Assert(request.Command == "omnisharp/executeCodeAction");
diff --git a/src/OmniSharp.LanguageServerProtocol/LanguageProtocolInteropHandler.cs b/src/OmniSharp.LanguageServerProtocol/LanguageProtocolInteropHandler.cs
index d211d9326f..cb61d19265 100644
--- a/src/OmniSharp.LanguageServerProtocol/LanguageProtocolInteropHandler.cs
+++ b/src/OmniSharp.LanguageServerProtocol/LanguageProtocolInteropHandler.cs
@@ -41,7 +41,7 @@ public static LanguageProtocolInteropHandler Factory(
     public class LanguageProtocolInteropHandler<TRequest, TResponse> : LanguageProtocolInteropHandler
     {
         private readonly IPredicateHandler _languagePredicateHandler;
-        private readonly Lazy<Task<Dictionary<string, IRequestHandler<TRequest, TResponse>[]>>> _exports;
+        private readonly Lazy<Dictionary<string, IRequestHandler<TRequest, TResponse>[]>> _exports;
         private readonly bool _hasLanguageProperty;
         private readonly bool _hasFileNameProperty;
         private readonly bool _canBeAggregated;
@@ -60,11 +60,10 @@ public LanguageProtocolInteropHandler(IPredicateHandler languagePredicateHandler
             _canBeAggregated = typeof(IAggregateResponse).IsAssignableFrom(metadata.ResponseType);
             _updateBufferHandler = updateBufferHandler;
 
-            _exports = new Lazy<Task<Dictionary<string, IRequestHandler<TRequest, TResponse>[]>>>(() =>
-                LoadExportHandlers(handlers));
+            _exports = new Lazy<Dictionary<string, IRequestHandler<TRequest, TResponse>[]>>(() =>LoadExportHandlers(handlers));
         }
 
-        private Task<Dictionary<string, IRequestHandler<TRequest, TResponse>[]>> LoadExportHandlers(
+        private Dictionary<string, IRequestHandler<TRequest, TResponse>[]> LoadExportHandlers(
             IEnumerable<Lazy<IRequestHandler, OmniSharpRequestHandlerMetadata>> handlers)
         {
             var interfaceHandlers = handlers
@@ -76,12 +75,12 @@ private Task<Dictionary<string, IRequestHandler<TRequest, TResponse>[]>> LoadExp
             // .Select(plugin => (plugin.Config.Language, plugin));
 
             // Group handlers by language and sort each group for consistency
-            return Task.FromResult(interfaceHandlers
+            return interfaceHandlers
                 // .Concat(plugins)
                 .GroupBy(export => export.Language, StringComparer.OrdinalIgnoreCase)
                 .ToDictionary(
                     group => group.Key,
-                    group => group.OrderBy(g => g.Handler).Select(z => z.Handler).ToArray()));
+                    group => group.OrderBy(g => g.Handler).Select(z => z.Handler).ToArray());
         }
 
         public string EndpointName { get; }
@@ -207,7 +206,7 @@ private async Task<object> GetFirstNotEmptyResponseFromHandlers(IRequestHandler<
 
         private async Task<object> HandleRequestForLanguage(string language, TRequest request)
         {
-            var exports = await _exports.Value;
+            var exports = _exports.Value;
             if (exports.TryGetValue(language, out var handlers))
             {
                 if (_canBeAggregated)
@@ -229,7 +228,7 @@ private async Task<object> HandleAllRequest(TRequest request)
                     $"Must be able to aggregate the response to spread them out across all plugins for {EndpointName}");
             }
 
-            var exports = await _exports.Value;
+            var exports = _exports.Value;
 
             IAggregateResponse aggregateResponse = null;
             var responses = new List<Task<IAggregateResponse>>();
diff --git a/src/OmniSharp.LanguageServerProtocol/LanguageServerHost.cs b/src/OmniSharp.LanguageServerProtocol/LanguageServerHost.cs
index b7b4f04549..8a12a9d667 100644
--- a/src/OmniSharp.LanguageServerProtocol/LanguageServerHost.cs
+++ b/src/OmniSharp.LanguageServerProtocol/LanguageServerHost.cs
@@ -113,10 +113,18 @@ public void Dispose()
             _cancellationTokenSource?.Dispose();
         }
 
+        private void Cancel()
+        {
+            try
+            {
+                _cancellationTokenSource.Cancel();
+            } catch (ObjectDisposedException){}
+        }
+
         public async Task Start()
         {
             var server = Server = await LanguageServer.From(_options);
-            server.Exit.Subscribe(Observer.Create<int>(i => _cancellationTokenSource.Cancel()));
+            server.Exit.Subscribe(Observer.Create<int>(i => Cancel()));
 
             var environment = _compositionHost.GetExport<IOmniSharpEnvironment>();
             var logger = _compositionHost.GetExport<ILoggerFactory>().CreateLogger<LanguageServerHost>();
@@ -125,7 +133,7 @@ public async Task Start()
 
             Console.CancelKeyPress += (sender, e) =>
             {
-                _cancellationTokenSource.Cancel();
+                Cancel();
                 e.Cancel = true;
             };
 
@@ -135,13 +143,13 @@ public async Task Start()
                 {
                     var hostProcess = Process.GetProcessById(environment.HostProcessId);
                     hostProcess.EnableRaisingEvents = true;
-                    hostProcess.OnExit(() => _cancellationTokenSource.Cancel());
+                    hostProcess.OnExit(Cancel);
                 }
                 catch
                 {
                     // If the process dies before we get here then request shutdown
                     // immediately
-                    _cancellationTokenSource.Cancel();
+                    Cancel();
                 }
             }
         }