Could not load type 'Microsoft.Azure.WebJobs.Host.Scale.ConcurrencyManager' from assembly 'Microsoft.Azure.WebJobs.Host

For me this was happening because Azure Functions Core Tools version mismatched due to upgradation of Visual Studio to latest version. Removing the Azure Function Tools from the system path C:\Users\user.name\AppData\Local\AzureFunctionsTools and Let Visual Studio automatically install Azure Functions Core Tools fixed the issue.

I had the same issue as below log.

Could not load type 'Microsoft.Azure.WebJobs.Host.Scale.ConcurrencyManager' from assembly 'Microsoft.Azure.WebJobs.Host, Version=3.0.25.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'.

It was due to my base image for azure functions was old. using the newer base image with below tag(mcr.microsoft.com/azure-functions/dotnet:3.4.2) has fixed my issue.

FROM mcr.microsoft.com/azure-functions/dotnet:3.4.2 AS base
WORKDIR /home/site/wwwroot
EXPOSE 80

FROM mcr.microsoft.com/dotnet/sdk:3.1.416 AS build
WORKDIR /src

This is not direct answer to your question but a tool that would answer it for you. As I had a lot of this kind of errors I have written a helper code to do just that. Its written for the .net framework but with minor changes you can have same thing on core.

       //folder where dependencies should be found
       var dir = @"C:\Repos\Project\bin"; 
       //dll or exe that you want to inspect
        var dll = @"C:\Repos\Project\bin\Project.dll"; 
        var asm = Assembly.ReflectionOnlyLoadFrom(dll);

        var stack = new Stack<Data>();
        stack.Push(new Data { 
           ReferencesPath = Array.Empty<Assembly>(), 
           Assembly = asm
        });
        List<AssemblyName> visited = new List<AssemblyName>();


        while (stack.Any())
        {
            var current = stack.Pop();
            var dependencies = current.Assembly.GetReferencedAssemblies();
            visited.Add(current.Assembly.GetName());
            foreach (var item in dependencies)
            {
                if (!visited.Any(x => x.FullName == item.FullName))
                {
                    Assembly dependency;
                    try
                    {
                        dependency = Assembly.ReflectionOnlyLoad(item.FullName);
                    }
                    catch
                    {
                        var path = Path.Combine(dir, item.Name) + ".dll";
                        dependency = Assembly.ReflectionOnlyLoadFrom(path);
                    }

                    if (dependency.GetName().Version != item.Version)
                    {
                        ; // put breakpoint here and inspect dependency 
   // and item when you find your dll in wrong version 
   // you can inspect current.ReferencesPath to see dependencies 
   // chain that causes the error
                    }

                    stack.Push(new Data
                    {
                        Assembly = dependency,
                        ReferencesPath = current.ReferencesPath.Concat(
new[] { current.Assembly }).ToArray()
                    });
                }
            }
        }



class Data
{
    public Assembly[] ReferencesPath { get; set; }
    public Assembly Assembly { get; internal set; }
}