The refactoring/rewrite of sequences used two saved states for arrays with Points of uncertainty, a beforeState at the very start of the array, and a priorState which the state prior to the current attempt to parse an occurrance.
In a code review it was observed that this beforeState prevents streaming by holding onto the I/O layer mark state for the entire array.
Arguably, the beforeState is not only unnecessary, but incorrect. Arrays don't need a PoU before the entire array that doesn't advance when occurrences are found. If the array is determined to exist, because at least one occurrence exists, then failure of the entire array causes the enclosing PoU to be determined, not an artificial one created at the start of the array.
Remove beforeState to fix.