LSTM Model - Validation Accuracy is not changing
One possible reason of this could be unbalanced data. You should have same amount of examples per label. And if you don't have that data, you can use Loss Weights. It is a parameter in model.compile(). You can learn more about Loss weights on google.
Also, I noticed you were using rmsprop as the optimizer. Try using Adam optimizer, as it is one of the best optimizer.
If, doing all of these I mentioned above, doesn't changes anything and the results are the same, remove the Dense() Layers and just keep 1 dense() layer, that is, just keep the last Dense Layer, and remove all the other Dense() Layers.
This will surely improve the model. But, if still it doesn't changes anything, then have a look here