The problem is that plain language is full of loopholes and double meanings. Legalese is hard to understand, but it tries to be precise and loophole-free.
The word "shall" in it can be replaced with "must" to make it more plain.
Edit:
This is some of the advice from the article: The use of "shall" creates confusion. To impose a legal obligation, use "must." To predict future action, use "will."