Cannot build to WebGL

[wesraph]

It's not possible to build to WebGL if using WebSocketTransport

Exception: /home/raph/Unity/Hub/Editor/2019.4.16f1/Editor/Data/il2cpp/build/deploy/net471/UnityLinker.exe did not run properly!

Failed running "/home/raph/Unity/Hub/Editor/2019.4.16f1/Editor/Data/il2cpp/build/deploy/net471/UnityLinker.exe" @"/home/raph/Unity/IsWebSocketDead/Temp/StagingArea/Data/Managed/response.rsp" 

stdout:
Fatal error in Unity CIL Linker
Mono.Linker.MarkException: Error processing method: 'MLAPI.Transports.NetEventType WebSocketTransport.WebSocketTransport::PollEvent(System.UInt64&,System.String&,System.ArraySegment`1<System.Byte>&,System.Single&)' in assembly: 'WebSocketTransport.dll' ---> Mono.Cecil.ResolutionException: Failed to resolve System.UInt64 MLAPI.WebSockets.WebSocketServerEvent::Id
  at Mono.Linker.Steps.MarkStep.HandleUnresolvedField (Mono.Cecil.FieldReference reference) [0x00018] in <c0c87e19439140b78d011a4c4a5bddd0>:0 
  at Mono.Linker.Steps.MarkStep.MarkField (Mono.Cecil.FieldReference reference) [0x0002d] in <c0c87e19439140b78d011a4c4a5bddd0>:0 
  at Mono.Linker.Steps.MarkStep.MarkInstruction (Mono.Cecil.Cil.Instruction instruction) [0x00044] in <c0c87e19439140b78d011a4c4a5bddd0>:0 
  at Mono.Linker.Steps.MarkStep.MarkMethodBody (Mono.Cecil.Cil.MethodBody body) [0x000e9] in <c0c87e19439140b78d011a4c4a5bddd0>:0 
  at Unity.Linker.Steps.UnityMarkStep.MarkMethodBody (Mono.Cecil.Cil.MethodBody body) [0x00001] in <8770b367edc74e678284d672346206ea>:0 
  at Mono.Linker.Steps.MarkStep.ProcessMethod (Mono.Cecil.MethodDefinition method) [0x001ca] in <c0c87e19439140b78d011a4c4a5bddd0>:0 
  at Unity.Linker.Steps.UnityMarkStep.ProcessMethod (Mono.Cecil.MethodDefinition method) [0x00041] in <8770b367edc74e678284d672346206ea>:0 
  at Mono.Linker.Steps.MarkStep.ProcessQueue () [0x00021] in <c0c87e19439140b78d011a4c4a5bddd0>:0 
   --- End of inner exception stack trace ---
  at Mono.Linker.Steps.MarkStep.ProcessQueue () [0x00052] in <c0c87e19439140b78d011a4c4a5bddd0>:0 
  at Mono.Linker.Steps.MarkStep.ProcessPrimaryQueue () [0x00019] in <c0c87e19439140b78d011a4c4a5bddd0>:0 
  at Mono.Linker.Steps.MarkStep.Process () [0x0013c] in <c0c87e19439140b78d011a4c4a5bddd0>:0 
  at Mono.Linker.Steps.MarkStep.Process (Mono.Linker.LinkContext context) [0x0000e] in <c0c87e19439140b78d011a4c4a5bddd0>:0 
  at Unity.Linker.Steps.UnityMarkStep.Process (Mono.Linker.LinkContext context) [0x00058] in <8770b367edc74e678284d672346206ea>:0 
  at Mono.Linker.Pipeline.ProcessStep (Mono.Linker.LinkContext context, Mono.Linker.Steps.IStep step) [0x0000e] in <c0c87e19439140b78d011a4c4a5bddd0>:0 
  at Unity.Linker.UnityPipeline.ProcessStep (Mono.Linker.LinkContext context, Mono.Linker.Steps.IStep step) [0x00018] in <8770b367edc74e678284d672346206ea>:0 
  at Mono.Linker.Pipeline.Process (Mono.Linker.LinkContext context) [0x00014] in <c0c87e19439140b78d011a4c4a5bddd0>:0 
  at Unity.Linker.UnityDriver.Run () [0x0009b] in <8770b367edc74e678284d672346206ea>:0 
  at Unity.Linker.UnityDriver.RunDriverWithoutErrorHandling () [0x00007] in <8770b367edc74e678284d672346206ea>:0 
  at Unity.Linker.UnityDriver.RunDriver () [0x00002] in <8770b367edc74e678284d672346206ea>:0 
stderr:

UnityEditorInternal.Runner.RunProgram (UnityEditor.Utils.Program p, System.String exe, System.String args, System.String workingDirectory, UnityEditor.Scripting.Compilers.CompilerOutputParserBase parser) (at /home/bokken/buildslave/unity/build/Editor/Mono/BuildPipeline/BuildUtils.cs:126)
UnityEditorInternal.Runner.RunManagedProgram (System.String exe, System.String args, System.String workingDirectory, UnityEditor.Scripting.Compilers.CompilerOutputParserBase parser, System.Action`1[T] setupStartInfo) (at /home/bokken/buildslave/unity/build/Editor/Mono/BuildPipeline/BuildUtils.cs:71)
UnityEditorInternal.AssemblyStripper.RunAssemblyLinker (System.Collections.Generic.IEnumerable`1[T] args, System.String& out, System.String& err, System.String linkerPath, System.String workingDirectory) (at /home/bokken/buildslave/unity/build/Editor/Mono/BuildPipeline/AssemblyStripper.cs:168)
UnityEditorInternal.AssemblyStripper.StripAssembliesTo (System.String outputFolder, System.String& output, System.String& error, System.Collections.Generic.IEnumerable`1[T] linkXmlFiles, UnityEditorInternal.UnityLinkerRunInformation runInformation) (at /home/bokken/buildslave/unity/build/Editor/Mono/BuildPipeline/AssemblyStripper.cs:159)
UnityEditorInternal.AssemblyStripper.RunAssemblyStripper (UnityEditorInternal.UnityLinkerRunInformation runInformation) (at /home/bokken/buildslave/unity/build/Editor/Mono/BuildPipeline/AssemblyStripper.cs:303)
UnityEditorInternal.AssemblyStripper.StripAssemblies (System.String managedAssemblyFolderPath, UnityEditorInternal.BaseUnityLinkerPlatformProvider unityLinkerPlatformProvider, UnityEditorInternal.IIl2CppPlatformProvider il2cppPlatformProvider, UnityEditor.RuntimeClassRegistry rcr, UnityEditor.ManagedStrippingLevel managedStrippingLevel) (at /home/bokken/buildslave/unity/build/Editor/Mono/BuildPipeline/AssemblyStripper.cs:180)
UnityEditorInternal.IL2CPPBuilder.Run () (at /home/bokken/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:490)
UnityEditorInternal.IL2CPPUtils.RunIl2Cpp (System.String stagingAreaData, UnityEditorInternal.IIl2CppPlatformProvider platformProvider, System.Action`1[T] modifyOutputBeforeCompile, UnityEditor.RuntimeClassRegistry runtimeClassRegistry) (at /home/bokken/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:235)
UnityEditor.WebGL.WebGlBuildPostprocessor.CompileBuild (UnityEditor.Modules.BuildPostProcessArgs args) (at /Users/bokken/buildslave/unity/build/PlatformDependent/WebGL/Extensions/Unity.WebGL.extensions/BuildPostprocessor.cs:387)
UnityEditor.WebGL.WebGlBuildPostprocessor.PostProcess (UnityEditor.Modules.BuildPostProcessArgs args) (at /Users/bokken/buildslave/unity/build/PlatformDependent/WebGL/Extensions/Unity.WebGL.extensions/BuildPostprocessor.cs:932)
UnityEditor.Modules.DefaultBuildPostprocessor.PostProcess (UnityEditor.Modules.BuildPostProcessArgs args, UnityEditor.BuildProperties& outProperties) (at /home/bokken/buildslave/unity/build/Editor/Mono/Modules/DefaultBuildPostprocessor.cs:29)
UnityEditor.PostprocessBuildPlayer.Postprocess (UnityEditor.BuildTargetGroup targetGroup, UnityEditor.BuildTarget target, System.String installPath, System.String companyName, System.String productName, System.Int32 width, System.Int32 height, UnityEditor.BuildOptions options, UnityEditor.RuntimeClassRegistry usedClassRegistry, UnityEditor.Build.Reporting.BuildReport report) (at /home/bokken/buildslave/unity/build/Editor/Mono/BuildPipeline/PostprocessBuildPlayer.cs:340)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr) (at /home/bokken/buildslave/unity/build/Modules/IMGUI/GUIUtility.cs:197)

Steps to reproduce the behavior:
Create a new 3D Project (Unity 2019.14.16)
Import MLAPI with MLAPI-installer.unity
Install MLAPI v11.11.4 (also tried with v12.1.7)+ WebSocketTransport (latest from the installer)
Create a new NetworkingManager with WebSocket as transport
Build to WebGL

OS: Archlinux (btw)
Unity Version: 2019.4
MLAPI Version: v11.11.4 and v.12.7
MLAPI Commit: [e.g. https://github.com/MidLevel/MLAPI/commit/c102935df1d7e0928283b48948fe96e5d96dd961]