The loss is zero all the time, when I fine turning myself datasets, which coco format

The loss is zero all the time, when I fine turning myself datasets, which coco format.


<img width="1377" alt="image" src="https://github.com/microsoft/GLIP/assets/25846975/ef51af2d-b626-4e9a-94b5-064b9e35ba7a">

```[tasklist]
### Tasks
```

why is this happen???