I was reluctant to reply seeing the vitriol unleashed in my absence.
The media remote I am using is a generic USB 2.4ghz one. It doesn't even have a model number it is so generic, and it is detected as a keyboard. I will not be changing the remote as it works perfectly on other LE installs and devices, and as a result I have several. The remote is not the issue.
This is why in the OP I linked to other threads with users encountering similar bugs caused by LE's handling of keyboard power button presses. OSMC works fine with this remote too across all hardware, so this issue is definitely localised to LE on this NUC.
As mentioned in the OP, I have tried the methods linked therein.
If anyone has any ideas that aren't in the threads I linked, please do reply. Let's try and keep it on topic this time; if you have a personal opinion about me that is not relevant to troubleshooting this issue.