laibsch

You should of course monitor the temperatures now to see if the board becomes abnormally hot (use your hand or the programs sensors or btop, for example).  That being said, a quick web search suggests to me that you are simply seeing a software problem AKA bug.  I suggest you open a bug ticket on the Armbian bug tracker and patiently wait for the board maintainer to have a look into the issue.
 
https://www.armbian.com/nanopi-neo-2/ lists https://github.com/spendist as the maintainer for your board.  Maybe you can send an e-mail?
 
sources:
https://forum.armbian.com/topic/9501-opzero-h5-after-update-41917-the-cpu-temperature-is-wrong/ https://community.nxp.com/t5/i-MX-Processors/IMX8MP-not-able-to-read-Thermal-zone0-temperature/m-p/1655665 https://community.nxp.com/t5/QorIQ/Temperature-is-not-available-at-sys-class-thermal-thermal-zoneX/m-p/1343009