Using SMP causes build failures to stop showing on subsequent builds (webpack watchdog)

[An631]

While using SMP in our webpack configuration, if I force a failure like this:

const value: string = {}

Type '{}' is not assignable to type 'string'.ts(2322)

and then do an initial build, the type check will fail.
However, if I then save any of the code files to trigger a subsequent build (watchdog build) the build becomes successful.

Somehow the SMP plugin is swallowing the errors for the watchdog builds.
I am using ForkTsCheckerWebpackPlugin to separate my type checking which I believe some people have reported as related
to this issue here

This is my plugin config and version:

{
      async: false,
      typescript: {
        configFile: 'tsconfig.srconly.json',
        diagnosticOptions: {
          semantic: true,
          syntactic: true,
          declaration: true,
          global: true,
        },
      },
      eslint: {
        files: "./src/**/*.{ts,tsx}",
      }
}

"fork-ts-checker-webpack-plugin": "^6.3.4",

Example of the problem:

Of course if I remove the SMP wrapper from my webpack config it all works as normal.