The word shall is rarely used correctly. Shall have many different meanings in which is beyond the meaning of an imperative "must". It has been identified as a very common error in contracts and legal documentation, where shall is used instead of may, must, or even when, giving a direction, stating circumstances, negating a right or duty, expressing an intention.
Use "will", "must" instead of "shall"
"Plain language experts suggest avoiding using shall as it is rarely used in one consistent meaning. Modern legislation in many jurisdictions have stopped using shall now" (Modernising Construction Contracts Drafting – A Plea for Good Sense , https://www.irbnet.de/daten/iconda/CIB18995.pdf).