VS Code problem with a variable defined in .py file


I am using VS Code with Robot Framework Language Server and Robocorp Code. Now I faced an issue where I have following variables defined in .py file:

CORE_PATH = os.path.dirname(os.path.realpath(file))
TEST_SYSTEM_PATH, _ = os.path.split(CORE_PATH)
LIBRARIES_PATH = os.path.join(TEST_SYSTEM_PATH, “Libraries”)

In test.robot file TEST_SYSTEM_PATH variable is shown as Undefined variable, other two variables are ok.

The variable is considered to be ok in VS Code if it is defined as follows:
temp_path, _ = os.path.split(CORE_PATH)
TEST_SYSTEM_PATH = temp_path

So is this an issue in Robot Framework Language Server or Robocorp Code? Or something else?