Hi,
After others thoughts in case I am missing something obvious and to help others if they are having the same issues, I have done attended upgrades multiple times without issue but 25.12.5 seem problematic on a Raspberry Pi 4 SD card install at least.
I do the upgrade as normal the whole router fails, I can't get in to it at all the lights are on but nothing is working. I rebuild the router from scratch (imaging the SD on my PC), then find that Luci Stats and VNStats is not working, turns out the connected SSD drive where I store them has been overwritten with the boot and root partitions image - no idea how that can even happen, so I rebuild that and got everything working.
Kept having connection issues daily for over a week often needing a reboot, rebuilt again, and again the SSD it overwritten with the standard image - but the failures continue.
Do some further investigations and not sure if this is something I added and it been lost, but it would be useful for in to be as an in default config.txt, as the "usb_max_current=1" option was missing, thus the USB ports are running at a max of 600ma shared not 1.2A - adding this stops the network instability so looks to be power related due to the network dongle and SSD requirements.
But... I still keep having odd things then get to the point I cannot login (via terminal or web), rebuild and find the the root drive is only 76Mb not the 100Mb plus it normally is. Again no idea why this has happened and is a problem for this build, as can't see anything in the release notes.
So I look at how to extend the rootfs overlay - there are so many different options and page re how to do it a nightmare, tried one page and it or my understanding of it trashed the router again. Rebuilt and then found the "Openwrt SD Card Wiki" and managed to get the partition extended from those instructions. But again this final rebuild overwrote the SSD again and I still have no idea how or why it can do that, its never happen on previous biulds or how to stop it from happening on future upgrades, as the 2 drives are logically separate?
Hope that above may help other RPI Openwrt users.