Detectron2 throwing "Non-existent config key" error on CPU even though the key is present in config.yaml

I have trained Detectron2 for Page Layout Detection on a PC _with_ GPU and it is giving satisfactory results.

If I try to use the trained model on _non-CUDA_ Detectron2 environment on same PC, or a _non-GPU_ PC I get the error:

```
raise KeyError("Non-existent config key: {}".format(full_key))
KeyError: 'Non-existent config key: MODEL.ROI_BOX_HEAD.FED_LOSS_FREQ_WEIGHT_POWER'
```

I have checked the config.yaml and it has:

```
MODEL:
ROI_BOX_HEAD:
FED_LOSS_FREQ_WEIGHT_POWER: 0.5
```

I have tried using pre-trained models with the non-GPU PC and they perform fine, only my own model raises the error specifically on non-GPU systems. I need to be able to use the trained model on a non-GPU work laptop.

Reproduce the failure on a non-CUDA environment using the reported config.yaml and compare how the configuration is loaded with the GPU environment. Trace where MODEL.ROI_BOX_HEAD.FED_LOSS_FREQ_WEIGHT_POWER is registered or rejected; done means the trained model loads and runs on a non-GPU PC without this KeyError.

Written by the indexing model from the issue text.