What's the model number of your extender? What's the light status? Can you get internet from your router directly? You may unplug the extender to test.

It's working as standard router or 4G router? What's the primary connection? Is the 4G connection still working?

There is risk if the voltage exceed the standard

Make sure you reset the router successfully. Do you still find the tplink wifi on your computer? Try login from your phone or pad. What operation mode you want to set up btw?

Does it happen every time after you turn off and on the power? Did you try manually push the reset button on the back of the router?

There is not Time settings when the 802N works in extender mode. It's available in router mode. so I think log time has nothing to do with the system time. As for why it shows the time as 2015, I...