Hi my router hard reset by itself few times over the past two months. Even a powrr off and on will hard reset sometimes. Is it power adapter failure? I got the latest firmware on the router AX82U.

Sometime using the latest version of firmware may not fix the issues. Try rollback to older version.

If the router still under warranty then send for RMA, if not then you need to buy a new router.

Hope this helps...

Well, router chipset especially high end models tends to run quite hot. It wasn't a problem when the device is new. However with years of usage, the thermal pad which are used to transfer heat between the chip and heatsink probably degraded and unable to perform at it's maximum efficiency. It's the same thing with high performance laptop and pc.