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

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

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.