Hello,
I recently got a Nanopi M4v2 on which I installed Armbian Buster current and updated the system, including kernel.
After a few hours the board would crash, requiring a power cycle.
Aftet reading this thread I decided to try a fixed frequency, so I left it at 2GHz. With a fixed clockspeed I ran stress tests, several runs of sbc-bench, browser benchmarks, used it to open documents in Libreoffice, watched videos using the browser, etc. and it was totally stable for over 5 days straight.
I only had problems with Chromium crashing, but Firefox (or equivalent) worked fine.
I changed the max and min clocks to defaults and it locked up about 4 hours later.
The board was working headlessly and I accessed it remotely using xrdp or dwservice.net.
I don't have it connected to UART at the moment because I don't have another computer nearby to connect it to where the board is placed, but if it helps I can find a way to connect it and give you the output.