I finally solved the frequent crashes of my AC-RT68U (post #175) by flashing the latest greatest Asus stock firmware for my router (3.0.0.4.384_10007). I didn't try Merlin 382.2-Beta2 which may also have solved it. It is nice to have some stability back again and see what stock looks like these...
Thanks for helping out! Its winter here and the AC68U has been residing in a well ventilated area ever since I got it so the temperatures are not really an issue I think (see temperatures.png).
Also I don't have any USB devices connected. I use the AC68U just for basic network functionality in...
My AC68U that ran 380.65_4 was all of a sudden plagued by reboots so I upgraded it to see if 380.69_0 would fix these. However that was not the case. I restored factory defaults after the upgrade and manually updated the settings via the UI.
The reboots are most likely caused by Android 8.1.0...