Short version: after one month emailing back and foth and arguing with Asus:
I got refund a free new/repaired ZF8 in exchange to my defect and BOOTLOADER UNLOCKED phone.
first of all: I bought the phone for my GF. It was used with a unlocked bootloader and rooted, but younger than 2 years, so theoretical in warranty.
First I fullfilled RMA formular and send device to Asus.
In the beginning they declined the phone because "the device is not covered by warranty, because the given issue is a softwareproblem and thus not covered by warranty.
Then the send my a cost estimate over 528,48€ for repair. Thats hillarious, almost the price of a new phone.
I send an email and explained the issue while claiming it's a hardware issue. In this email I linked these forums:
While i was scrolling around on the phone in suddenly died on me. From scrolling the web to absolute dead in my hands. It does not charge, it is not recognized by a PC, it does not go in boot mode or anything like that - absolutely dead. I had it for 1 year and will not fix it as fixing cost...
Hi, A week ago I was using my < 4 months old Zenfone 8 while traveling in Germany, and at 19% battery the screen turned black. I went back home, tried charging it for as long as possible, it was staying cold and never showed any sign of life...
and told them to read carefully.
Answer: No warranty, because of unlocked bootloader.
Me: Unlocked bootloader has nothing to do with hardware issues. Have you read in forums?
(Meanwhile ignoring emails refering to processing fees and the cost estimate.)
Asus: Unlocked bootloader, means no warranty. Try to contact your seller and ask him for refund.
Me: First I don't know how the reseller could help, becaus it's Asus fault. Second I don't care about warranty, fact: the device was faulty immediately after it left the production. I payed for the device, so Asus has to deliver. Maybe you didn't get the issue correctly so please explain it to me:
Why has my phone died?
Asus: We will check your issue and we get in touch again.
Asus: Dear customer, we will offer you a free repair.
Now the repaired or maybe new phone is on the way to me.
Guys stay strong!! Take the time, It's worth it!!