Following a recent update to the Zenfone 6, some owners have been reporting system stability problems including frequent crashes/restarts, network connectivity problems, and bootloops. According to a recent statement issued by an ASUS representative on the company's ZenTalk forums (spotted by PiunikaWeb), the issue is a hardware fault in affected devices which is triggered by the update.

According to forum moderator Anders_ASUS (presumed to be Anders Haby, community manager for ASUS' Zentalk forums), there is no fix for those that experience the issue, short of a hardware repair or replacement:

I'm really sorry but the solution to this issue is to contact the service center. The .167 update triggered a motherboard malfunction which only some units have had and it's natural that their owners find their way here.
"Fixing" it with software would only cover up a hardware related issue which will most likely popup later with some other update. You will get a new motherboard when you send it in and I'm sorry you were one of the affected people. You can discuss how to solve this as smoothly as possible with your service center.

The software which triggered this problem is version 16.1220.1906.167, and at the time of its release, the changelog primarily focused on camera improvements, though a few general system details like "improved call quality" and "optimized power consumption" could imply deeper changes.

It isn't immediately clear how many devices are affected by this issue. While there are a handful of reports at ASUS' forums, availability for the Zenfone 6 has been limited, both in terms of the markets it can be purchased in and the quantity available.

ASUS' Zenfone 6 ended up being one of the biggest smartphone surprises of the year, earning a generally positive review from most outlets — including us. Among the only known drawbacks were the lack of US availability. While that was resolved just yesterday, we hope that the US model of the phone is unaffected by hardware issues such as these.