Communications liabilities in battle: Is there an example of resources (living or otherwise) which could have been pivotal in battle had appropriate communications been able to reach them?

Three examples come to mind: Neuve Chapelle and Loos in 1915, and some actions in the Somme Campaign in 1916.

At Neuve Chapelle, the British penetrated the German first line, but were ordered to halt once that position was taken, before advancing on Aubers Ridge. Orders were sent for the infantry to move forwards, but they arrived almost an hour late, and the Germans were able to dig in and hold the ridge, while counter-attacking the British.

At Loos, the German first position was penetrated in many areas, but BEF C in C Sir John French had kept the reserve divisions too far back. Again, the Germans were able to reinforce their second position, and the reserves arrived only to attack strong, prepared defenses, and were badly cut up.

Two examples from the Somme campaign come to mind, July 1st and July 14th. On July 1st, the British XIII and XV Corps on Fourth Army's right wing penetrated the German first line. The French to their right did the same, and a gap opened towards Longueval that could have unhinged the German positions. Walter Congreve, GOC XIII Corps requested to be allowed to go forwards in cooperation with the French, but the British Cavalry were positioned further north, away from where the gap was. Delays allowed the Germans to send reserves to plug the gap, and even had the cavalry been available, Henry Rawlinson, GOC 4th Army would not allow Congreve to move ahead, XIII Corps having reached all of it's objectives for that day.

On July 14th, when the British launched a set-piece attack on the German second position around Bazentin Ridge, the Hyderabad and Deccan Cavalry Brigades were available to exploit any gaps in the German line, which they did. At the cost of c. 7 dead, they captured a number of prisoners and machine guns, and established a foothold in the south-eastern part of High Wood. Unfortunately the infantry that should have been supporting them were unaware, and increasing counterattacks led the Indians to withdraw in good order before the day's end. High Wood was subsequently the site of bloody, piecemeal fighting for the next two months of the battle.