Complex sentence: The advance had been held up at Juniper Cottage and German guns in a gap near Judge Copse also held up the infantry; a reserve platoon was sent up but was also unable to clear the copse.
Split into simpler sentences: The advance had been held up at Juniper Cottage and German guns in a gap near Judge Copse were holding up the infantry. A reserve platoon was sent up but was also unable to clear the copse.