Many Zenfone6 users in Japan posted sudden death approx. 2 years use. I visited several local repair shops and heard that all of these repair shop owners experienced this issue Inquiry. Unfortunately, they did not have good solution for permanent measurement. Similar reports appear in google search suggestion even just typing "zenfone 6".
I also really like its performance. If the phone doesn't fail again after repair by ASUS genuine service factory, it's worth to pay. But it is unclear as we have no clear explanation.