The leading assumption is it's malware that got onto the router through a security vulnerability. Were you using AiCloud 2.0? Did you have Cloud Disk, Smart Access and or AiCloud Sync enabled? The current working theory is that AiCloud was compromised via a security vulnerability and malware injected onto the router. It is possible this WiFi getting corrupted issue is related. More discussion here:
This malware damaging Asus routers has to be described in a sticky thread with a warning sign! Update: Asus is releasing patched firmware for multiple models. Check for firmware updates! The changelog for most firmware releases contains the following: 1. Strengthened input validation and data...
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Asus has released firmware updates referencing a fix for AiCloud for most of their routers in the past week. Asus-Merlin firmware likewise has been updated with an AiCloud fix in recent days. The RT-AX86U (and RT-AX86S) routers are still awaiting an update. Its
rumored (unverified) there may be an update this week for the that router.