Issue while training Donut model for parsing with custom decoder and tokenizer
Hey all, I was trying to train donut model for parsing, which contains Arabic(only) information, in order to achieve this i had collected `Arabic corpus` from various sources and then trained,
1. `Mbart Tokenizer` for arabic corpus.
2. `Mbart decoder` with the same dataset.

Initially the model was training well meaning the loss was decreasing gradually but, during Validation, all my dataset tokens are predicting as `<UNK>` tokens. Because of this the `Normed ED` value is above `0.9` but still the loss is decreasing. 

Is there anything I am missing out , any inputs will help a lot. @gwkrsrch , @Vadkoz ,@NielsRogge
Thanks regards.
Hi @akashlp27 

As per our [issues guidelines](https://github.com/huggingface/transformers/blob/main/ISSUES.md), we reserve GitHub issues for bugs in the repository and/or feature requests. For any other matters, we'd like to invite you to use our [forum](https://discuss.huggingface.co/) 🤗

However, you might want to take a look
https://github.com/huggingface/transformers/issues/18190#issuecomment-1273482690
https://github.com/huggingface/transformers/issues/18190#issuecomment-1216584872
(Not sure though)<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.