Wikipedia states..."he was interned [as a illegal immigrant] in a Swiss refugee camp near Zurich in 1942. He had already been in frail health, and was treated for a throat infection at the local hospital. Schmidt complained of chest pains, but this was dismissed and he was discharged on Nov 14. Just two days later, while attempting to recover at the nearby Walzegg Inn, the famous singer collapsed. [Allegedly] He was to have been issued a work permit the following day, so he would have been able to move freely within Switzerland. A plaque is mounted at the inn where he died"
[as a illegal immigrant ] is my insert from other reading... which also revealed he had an American passport and was well known.
[Allegedly] is speculation on my part.
Further google reading...
"Because he was only 4' 9" [4' 11'] tall, he was unable to perform in operas but was extremely well suited for radio and for making phonograph records."
[4' 11"] from other reading.
"Joseph Schmidt who in the 1030's was known as the 'German Caruso', singled out for praise by no less than Joseph Goebbels (1933), propaganda minister of the Third Reich, was actually born in Romania, to Jewish parents."
"He was one of the worlds greatest tenors."