Gladiolus is commonly attacked by gladiolus thrips, which can be difficult to see but feed on the shoots and flowers. They will often result in silver-streaked foliage, stunted plants, and flowers that fail to open. The thrips may have nested in your corms and will reappear next year unless you take steps to combat them now.
Dig the corms in autumn and store them in an unheated garage or shed (with temps about 35-40 F.). This should help kill off any of the remaining pests. Control thrips during the growing season with insecticidal soap or neem oil. Here is more information on controlling thrips: https://www.gardeningknowhow.com/plant-problems/pests/insects/controlling-thrips.htm