Mask dimension expansion might be wrong
https://github.com/huggingface/transformers/blob/17292440c069118fbdb992b9a17da2098fab5b87/src/transformers/models/reformer/modeling_reformer.py#L845

I feel that the way mask is expanded here might be wrong. More specifically, I feel that mask need to be repeated by the number hashes and splited into chunks before running gather. 

Please look into it and let me know if I misunderstood. Thank you so much!
cc @ArthurZucker <|||||>Hey! Do you happen to have found an error or any discrepancy ? I am not very familiar with this model but if you have a reproduction script or something to help me work on this, would be appreciated! <|||||>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.

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