I have seen this happen from time to time - and on varying NUC models - but never consistently as you have described. Are you running the latest BIOS (73) for your NUC?
Oh no, that is way, way, way! out of date. That is BIOS 51. The latest is BIOS 73. I believe that this explains why you are having this issue.
You can download the latest BIOS from here: https://downloadcenter.intel.com/download/28951/BIOS-Update-BECFL357-86A-?product=126140. Download the Windows 10 (.msi) file and then double-click on it to start its install. It will reboot your system, install the BIOS, reboot your system again and let Windows start back up.
Thanks Scott, I have now downloaded 73 from the website and we installed today, tested a reboot and looks to have fixed the problem! So super cool and thanks for your help. If it still plays up I will come back