DotNetCore dotnet.cli unmet requirements

Upgraded from old TeamCity 9.1.6 to latest 2017.2.3, in old installation, DotNetCore CLI was working; we have around sixty projects reliant on it.

After upgrade, I'm seeing unmet requirements:

• DotNetCore exists 
• DotNetCore_Path exists

I saw the old github post about the environment variable DOTNET_HOME, and needing dotnetcore in the PATH.

Home is set and shows in the agent environment variables, and the path shown includes the dotnet core directory (which is the default).

After the upgrade, there was an old "external" version of the dotnet CLI plugin (though it was disabled). I thought that may be the cause of the problem, and uninstalled it, but it made no difference.

I can't see anything leaping out in the logs, but I'm not sure whether I should be looking more closely at the agent log, or the server log.

The problem manifests with all agents.