Assume your input shape is [N, 25, 12], after the first Conv1d, it will become [N, 25, 3], while 3 is too short for next Conv1d with kernel_size=(4,).
Check https://pytorch.org/docs/stable/nn.html#torch.nn.Conv1d 51 for output shape of Conv1d and try padding or changing the stride. But I think 12 is just not enough.