Well, fixed it. It seemed I had 3 problems to fix:
1. Usage not being reported, because
2. Range or interference problems,
3. A strange on/off power switch which had to be pushed AND HELD IN FULLY for a few seconds before the power light came on. Then it could be released.
Following hours of researching and tests I found that the location of the router was no longer appropriate. I suspect its signal is weaker than when new, so its location is likely more critical now. I tested the signal strength in dBm off ALL the intruding wifi signals around my home and found that one neighbours signal was stronger and everywhere on channel 1 of 13. My router was struggling against it on Channel 11. My solution was to move my router near as possible to the neighbours strongest signal and repower it yet again.
Interestingly my router autoselected the SAME channel 1 as the most powerfull neighbours - but this seems to work well in its new position.
Moral of the story is that router position is everything. The router tends to auto select a new channel on restart which considers the channels and strengths of neighbouring signals over a short sampling time, the latter (signal strength) being effected by my routers position.
I also tested the 12V 1A router supply under load and it was fine, had suspected that would cause lower power output and multiple self resets seen earlier, but the supply was OK. Moving the router also meant it was plugged into the main phone socket rather than an extension using another filter.
