Had a similar experience with the last ship I bought. Trailer tires looked great, almost new I thought! Found out later they were the original tires on the Cobra, some 15 years ago! I got about 300 miles on those tires when the right one threw a 12” hunk of tread with one end still attached...............bam, bam, bam, it sounded like a helicopter! Removed the fender as though it was never there! The ship had seldom left the gliderport and tire pressure was down when I got the bird. I figured that 15 long cold winters with tires partially deflated, had weakened the flat spot area. Always seems to happen when a ship is sold and the trailer sees the road for the first time in many years. Tire guy told me those were 2 ply auto tires, he recommended 6 ply trailer tires............no more tire problems!
Cheers,
JJ