Inexplicable damage – Hankook S1 Evo2 inside

Hello together, in spring 2016 I bought four new BMW aluminium wheels and four new Hankook tyres. Hazards are on mixed tyres with VA 225/40/18, HA 255/35/18. The wheels are mounted on a BMW 325d Kombi (E91) with rear drive in summer, driving profile 90% highway straight out, rest inside. The wheels were driven about 60tkm, the rear had to be replaced before. Now I present an inexplicable damage to the inside of the left side of the wheel. n front wheel fixed. This expression does not exist all around, but almost half of the circumference. When driving, I did not notice anything about it, there were no significant extreme situations when driving or the like. The right tyre is absolutely flawless, even the rest of the profile of the affected tyre looks evenly. Basically, I was also very satisfied with the Hankooks except for this expression. Now the question, how can this happen? Too bad about the still good tire. In 2017, the car had received a chassis revision with brand parts and subsequent lane adjustment at the best address in the city. So I’m closing on the tire myself? Do you think it’s a good idea to write to Hankook? Thank you.