This could be due to the potential degradation of the casein in dairy which typically begins once a temperature above 105 degrees Fahrenheit is reached (most likely a failure in transportation cooling). After the casein is broken down it creates a quasi synthetic (casein does not exist naturally in homogenized combinations of sugar and fat) antimicrobial compound in combination with the other more stable proteins in the yogurt ultimately forming an interlinked "web" type structure. The naturally occurring bacteria within the yogurt is then slowly surrounded and suffocated by this new compound and creates a jelly like substance which will not commonly adhere to metallic surfaces. The yogurt is still perfectly fine to eat so long as you don't mind denatured proteins and dead bacteria.