Flutter: "packages pub" doesn't release flutter lock

When running flutter packages pub run build_runner watch to generate model classes and keep the generated code up to date with the change I make. I can't build or install or hot reload the project I'm working on.
When I pressed the run button in intellij to compile and install the app I get the following error:

Waiting for another flutter command to release the startup lock...

When I kill the build_runner process it starts compiling and installing the project.

If I start the build_runner watch when the project is already running on a device or simulator/emulator
I get the follow error when I make a change to the code:

Initializing hot reload...
Your application could not be compiled, because its dependencies could not be established.
The following Dart file:
  /Users/user/projects/project/lib/value_models/models.dart
...refers, in an import, to the following library:
  /Users/user/projects/project/lib/value_models/models.g.dart
Unfortunately, that library does not appear to exist on your file system.

Is there a way to start a separate process for the code generation so we can keep compiling and running our apps during development?