I can attest to sorbate allergies that started with my cheeks flushing, heart rate going up and coughing in 2006. In 2007 I broke a rib trying to suppress a cough after eating at a restaurant. I went on an elimination diet for 1 month eating only rice, then re-introduced fruits and veg, then meats and dairy products. By then I had worked out it was an additive because I reacted to yoghurt but not milk. Eventually a fruit juice gave the reaction. Since then I have avoided it as far as possible. However despite my best efforts sometimes one still gets exposed. The allergy has progressed to bronchospasm, upper airway obstruction and hypotension requiring 4l of IV fluids to restore. I now carry adrenalin (Epipen) on me.
 
Different countries contain sorbate in different things. In South Africa butter only contains salt, in Australia some butter contained sorbate. The same brand of ice-cream in South Africa does not contain sorbate but in America it does… - Josie (South Africa)

See Sorbate factsheet