Could not load file or assembly 'Microsoft.EntityFrameworkCore.SqlServer, Version=3.1.0.0

I am converting a Asp.net Core 3.0 to asp.net core 3.1. Everything works fine from visual studio 2019. However when I publish a deployment package and execute the web application from IIS I get the following error message: Application startup exception: System.IO.FileLoadException: Could not load file or assembly 'Microsoft.EntityFrameworkCore.SqlServer, Version=3.1.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60'. The located assembly's manifest definition does not match the assembly reference. (0x80131040) File name: 'Microsoft.EntityFrameworkCore.SqlServer, Version=3.1.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60'

Nuget package used: Microsoft.EntityFrameworkCore, Microsoft.EntityFrameworkCore.Relational,Microsoft.EntityFrameworkCore.SqlServer,Microsoft.EntityFrameworkCore.Tools Packages Installed: Microsoft.Net Core.1.0 - Windows Server Hosting, Microsoft.Net Core - 3.1.0 Preview 3 (x64), Microsoft.Net Core SDK 3.1.100(x64) from visual studio

IIS: Version 6.1 (Build 7601 Service Pack1)

I just had the same problem, turns out I had to clean the output folder. /bin/Release contained netcoreapp3.0 and netcoreapp3.1 and somehow it got mixed up. I just cleaned the sources in Azure DevOps and tried again and it worked.