Why is this warning message appearing?

Question

    if any(k in model_args.model_name_or_path for k in ("gpt", "opt", "bloom")):
        padding_side = "left"
    else:
        padding_side = "right"
    
    tokenizer = AutoTokenizer.from_pretrained(
        model_args.tokenizer_name if model_args.tokenizer_name else model_args.model_name_or_path,
        padding_side=padding_side,
        use_fast=model_args.use_fast_tokenizer,
        revision=model_args.model_revision
    )
    
    if tokenizer.pad_token_id is None:
        tokenizer.pad_token_id = tokenizer.eos_token_id
    
    ...


    trainer = Seq2SeqTrainer(
        model=model,
        args=training_args,
        train_dataset=dataset.train_dataset if training_args.do_train else None,
        eval_dataset=dataset.eval_dataset if training_args.do_eval else None,
        compute_metrics=dataset.compute_metrics,
        tokenizer=tokenizer,
        data_collator=DataCollatorForSeq2Seq(tokenizer, model=model)
    )

While using GPT2, during training, there are no warning messages, but during validation, the message as mentioned appears. As seen in the code, pad_token_id='left' and pad_token_id=eos_token_id are already set as required.

Why might this message be appearing during validation? Is there any additional task needed?