Every manufacturing process for just about everything imaginable pops a lemon out every so often. I like Shenko tires. I use the 230 Tour Masters on mine and I've never had an issue. Shenko is a Japanese owned company that manufactures in South Korea.
I've heard a few sportbike people complain about them and perhaps that's not the best usage for them but for the 750 Vulcan they're fine.
More than likely, yours is that once-in-a-blue-moon lemon.
Saddlebags, hard mounted
Fork mounted tool bag (now hard mounted)
Relocated rear turn signals
LED turn signals, brake lights and running lights
LED license plate frame
Engine Guard and Highway pegs
National Cycles Low Boy Heavy Duty windshield
Home made lowers (nice)
Custom seat (made by a local guy)
Iridium plugs (DPR7EIX-9)
Shenko 230 Tour Master tires at 11,123 miles
Splines lubed at 11,123 miles
Light bar with LED lights
Progressive 412 shocks