It was not a bug so removed unnecessary information.

The next version of Flex.1-alpha is released.
https://huggingface.co/ostris/Flex.2-preview

The solution is provided using custom pipeline by author of model which is working. Please refer the Model card for code.

However, it will be good to have this integrated in diffusers as core function.
In future other variants of Flux schnell may appear with similar functionality.