This is an issue directed at the Minecraft Bedrock protocol. When the client responds to a form it sends a ModalFormResponse packet which is normal. If the client closes the form and does not respond the response is "null" which is also normal. The issue here is when the client responds normally and does not close the form, for example just pressing a button on a Simple form, it will send two packets. One being the button pressed, and the other being null when the form was closed. This does not make sense because if there is any response at all then the form should be closed.

1) Send a ModalFormRequest packet to a client, lets assume with the data of a Simple form

2) Press a button on the form

3) The client will send back two ModalFormResponse packets instead of one, one response is the form data and the other is null because the form was closed. Like I mentioned above, if there is any response at all the form will be closed so the second response is completely unnecessary.