I am having wireless issues with Orcon's NF4V router, though it's probably not NF4V's fault, just wondering if anyone else's seeing similar issues.

The issue is that when iPhone goes to sleep, it disconnects WIFI (presumably to save power).
And whenever traffics are detected, it jumps back on WIFI and notification pops up I'm guessing with 802.11 beacon interval settings.

The above used to be seamless.

Now it is not. From time to time I can see that my phone is on 3G/4G when I turn it on, and worst of it all, it's really digging into my mobile data usage.

So much so that when I'm home I just turned the mobile data off.

I've tried the limited settings offered by Apple, from the most obvious reset network settings, to the most time consuming resetting the entire phone. I have also tested with a brand new iPhone as well.
Also tried less obvious settings like turning off WiFi assist, turning off Wifi Networking under Location's system services.

Can't say any of it made any difference.

I've been blaming Apple this entire time, but recent trip overseas it has worked brilliantly. So I'm wondering if there's an issue with this router?

Any ideas? What really haunts me is that it used to work so brilliantly that it never crossed my mind how much work it was all doing...