@Dinno Try positioning the device closer to the main router. 5GHz band is more susceptible to distance than the 2.4 GHz. If that persists use the web GUI of the device via browser.

Try opening UDP ports 500 and 4500 in the destination device. Also make sure this is enabled:

I am not familiar with the method that fing is using to determine whether a host is on/off line but you can try with another program to test the behavior - for example with Angry IP scanner.

Can you ping the IP address in question while the device is off ? Any replies from the ping command ?

I doubt that anyone can answer your question since v2 is pretty much new version and there is not enough feedback to tell, if there are any issues. I am using v1 and can tell, that so far it's stable...

@VfV " What possibly causes a TP-Link user to run out of toothpicks? (Answer: Doing hard resets) " - that's a good one :) Actually hard resetting the device can solve many bizarre issues as practice...