Complex sentence: Another delay was caused by Lieutenant-General Congreve the XIII Corps commander, being relieved due to illness on 10 August and be replaced by the XIV Corps staff under Lieutenant-General Cavan, which had to move from the Reserve Army front to take over.
Split into simpler sentences: Another delay was caused by Lieutenant-General Congreve the XIII Corps commander, being relieved due to illness on 10 August. He was replaced by the XIV Corps staff under Lieutenant-General R. Cavan, which had to move from the Reserve Army front to take over.