I had this problem a few times now with different boards each time. Basically everything works fine for a while and then after a month or two, adb is no longer working. The device does not show up on a connected computer, connecting is obviously also not working then.
The snapdragon boots normally. I can ssh into it and use it. Any idea how to debug or fix ADB? My solution last time was to reinstall everything from scratch. But that's just a wasted day...
There is no obvious pattern in when it stops working. I did not use apt-get or anything like that in a while.