Default [Q] Wifi works on other routers but not my own

I have a strange problem. I noticed that certain apps (mainly the system apps like Play and Maps) don't work when I'm connected to wifi on my home Asus AC66U router, even though the bars are blue.

What's odd is that those apps work on both 3G and on other wifi networks. That should mean there's a problem with the router somehow, but every other device (PC, laptop, another Android phone) works fine. This has also been a persistent problem so the router doesn't just need a reboot.

I used to run a custom ROM so there's a chance something got messed up when flashing updates, but I eventually did a factory reset and returned to stock. And I've tried clearing the system apps' caches of course. Any ideas?