Why does MassTransit.Serialization.SystemTextJsonMessageSerializer 8.0.3 thrown an exception when configuring the bus in .NET 4.6.2 + ASP .NET MVC - asp.net-mvc

Question

We have a .NET Framework 4.6.2 ASP .NET MVC application that configures MassTransit.RabbitMQ 8.0.3 in the Startup class
The code is below
var busControl = Bus.Factory.CreateUsingRabbitMq(cfg =>
{
cfg.UseNewtonsoftJsonSerializer(); //Also tried UseNewtonsoftRawJsonSerializer and without
cfg.Host(WebConfigurationManager.AppSettings["RabbitMQHost"], "/", h =>
{
h.Username(WebConfigurationManager.AppSettings["RabbitMQUsername"]);
h.Password(WebConfigurationManager.AppSettings["RabbitMQPassword"]);
});
});
This is the exception
System.TypeInitializationException
HResult=0x80131534
Message=The type initializer for 'MassTransit.Serialization.SystemTextJsonMessageSerializer' threw an exception.
Source=MassTransit
StackTrace:
at MassTransit.Configuration.SystemTextJsonMessageSerializerFactory.get_ContentType()
at MassTransit.Configuration.SerializationConfiguration.AddSerializer(ISerializerFactory factory, Boolean isSerializer)
at MassTransit.Configuration.SerializationConfiguration.AddSystemTextJson()
at MassTransit.Configuration.EndpointConfiguration..ctor(ITopologyConfiguration topology)
at MassTransit.RabbitMqTransport.Configuration.RabbitMqBusConfiguration..ctor(IRabbitMqTopologyConfiguration topologyConfiguration)
at MassTransit.RabbitMqBusFactory.Create(Action`1 configure)
at Startup.ConfigureMassTransit(IUnityContainer unityContainer) in C:\p\Startup.cs:line 79
at Startup.Configuration(IAppBuilder app) in C:\p\Startup.cs:line 59
Inner Exception 1:
TypeInitializationException: The type initializer for 'System.Text.Encodings.Web.DefaultJavaScriptEncoder' threw an exception.
Inner Exception 2:
TypeInitializationException: The type initializer for 'PerTypeValues`1' threw an exception.
Inner Exception 3:
FileNotFoundException: Could not load file or assembly 'System.Runtime.CompilerServices.Unsafe, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.
Inner Exception 4:
FileNotFoundException: Could not load file or assembly 'System.Runtime.CompilerServices.Unsafe, Version=4.0.4.1, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.
What I've tried
I read the Serialization section of the MassTransit 8 upgrade guide. I added UseNewtonsoftJsonSerializer. Same error.
I had a look at Microsoft's Migration guide from NewtonSoft.Json to System.Text.Json. Our web app includes both System.Text.Json and NewtonSoft.Json. I tried uninstall System.Text.Json but Masstransit requires that. We use NewtonSoft.Json in a lot of places in our code.
I found some assembly redirects in the .config files. I removed those but I still get the error.
Checked that System.Runtime.CompilerServices.Unsafe (6.0) is installed (as a nuget package)
Questions
Why am I getting this error and how to I fix it?
Other details
One of the errors mentions "DefaultJavaScriptEncoder" and another mentions "SystemTextJsonMessageSerializer".
The Webapp uses Unity 5.6.0 (and Unity.Abstractions 3.2.0, Unity.Container 5.6.0, Unity.MVC 5.0.12, Unity.WebAPI 5.3.0)
Using MassTransit 7.1.8 we do not have these problems.
Update 1
Not adding this as an answer because it's specific to my system.
I managed to fix this by adjusting / fiddling with the dependenyAssembly / bindingRedirect in the web.config file.
I remove System.Runtime.CompilerServices.Unsafe dependencyAssembly / bindingRedirect.
I added these dependencyAssembly / bindingRedirect (which I got from the exception message: change dependencyAssembly, run program, get exception, repeat)
Microsoft.Extensions.Logging.Abstractions
System.Diagnostics.DiagnosticSource
Microsoft.Bcl.AsyncInterfaces
System.Threading.Channels
<!--<dependentAssembly>
<assemblyIdentity name="System.Runtime.CompilerServices.Unsafe" publicKeyToken="b03f5f7f11d50a3a"/>
<bindingRedirect oldVersion="0.0.0.0-6.0.0.0" newVersion="6.0.0.0"/>
</dependentAssembly>-->
<dependentAssembly>
<assemblyIdentity name="Microsoft.Extensions.Logging.Abstractions" publicKeyToken="adb9793829ddae60"/>
<bindingRedirect oldVersion="0.0.0.0-3.1.18.0" newVersion="3.1.18.0"/>
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="System.Diagnostics.DiagnosticSource" publicKeyToken="cc7b13ffcd2ddd51"/>
<bindingRedirect oldVersion="0.0.0.0-6.0.0.0" newVersion="6.0.0.0"/>
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="Microsoft.Bcl.AsyncInterfaces" publicKeyToken="cc7b13ffcd2ddd51"/>
<bindingRedirect oldVersion="0.0.0.0-6.0.0.0" newVersion="6.0.0.0"/>
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="System.Threading.Channels" publicKeyToken="cc7b13ffcd2ddd51"/>
<bindingRedirect oldVersion="0.0.0.0-6.0.0.0" newVersion="6.0.0.0"/>
</dependentAssembly>