There are three themes
United States and Postal Codes:
Unequivicably STATE state that one refuses to get along= SC,OR,NH, AR,MO, NY which includes Arizona but not Louisiana or Montana.
Of the 3 clues that are states ARIZONA = ICE1DArkansas[---] is the only one in the themer.
Chemical Symbols
PERIODIC bouts of sleepwalking = S,O,Mn, Am, B,U,Li, SM of which includes Manganese but not Tungsten or Plutonious. Of the 3 clues that are elements Manganese = CREAM51DManganese[-----] is the only one in the themer.
International Airports
The study of the progression of conveyances of information (such as AIR, print, or broadcast) over time MED, IAH, IST, ORY = Medina Saudi Arabia; Prince Mohammad Bin Abdulaziz + Houston, George Bush Intercontinental + Istanbul International + Paris, Ory International but doesn't include either Barcelona, J.A. Anzoategui International nor Chicago, O'Hare International. Of the 3 clues that are International Airport only Houston, George Bush Intercontinental = FLAVOR45DHouston, George Bush Intercontinental [------] is in the themer.
Take those answers ICE1DArkansas[---] + CREAM51DManganese[-----] + FLAVOR45DHouston, George Bush Intercontinental [------] and there is one clue, 19D19DRocky Road[------], that is an ICE1DArkansas[---] CREAM51DManganese[-----] FLAVOR45DHouston, George Bush Intercontinental [------]. 19D19DRocky Road[------] = Rocky Road = ORDEAL19DRocky Road[------] . And that is the answer.
The other trios of clues yield BIG23DMontana[---] BAND63APlutonium[----] MUSIC50AChicago, O'Hare International[-----] => SWING TIME => RECESS41ASwing Time[------], and THUMB8ALouisiana[-----] NAIL4ATungsten[----] PIC14DBarcelona, J.A. Anzoategui International[---] => ICON => HERO9DIcon[----] but as those involve items that were not in any themers they do not count.