My Big Jim and King Jim rubber coming off..

I've had these about 6 months and 1-2 rides a week. Last ride I noticed a knob ripped off down to the casing and the side walls starting to 'hair' off. (the rubber coming off in long, hair like strands). The tires have lots of tread on them. It seems strange that they're both doing this. Has anyone had the same experience? These are not seconds.....
Thanks
SB