The type or namespace name 'EnsLib' does not exist in the namespace 'InterSystems' for .Net Gateway

I'm using this Dockerfile to build .Net Gateway with my PEX BS. It works fine. If I change the image reference here to store/intersystems/iris-community:2021.2.0.617.0 in line 8 (so update from 2020.2 to 2021.2) it fails to build with:

KafkaConsumer.cs(4,20): error CS0234: The type or namespace name 'EnsLib' does not exist in the namespace 'InterSystems' (are you missing an assembly reference?) [/source/KafkaConsumer.csproj]

KafkaConsumer.cs(9,34): error CS0246: The type or namespace name 'BusinessService' could not be found (are you missing a using directive or an assembly reference?) [/source/KafkaConsumer.csproj]

On this line:

RUN dotnet publish -c release -o /app

Any idea why this might happen?