Weird intermittent connectivity issue to Google IP addresses

Installing and Using OpenWrt
1

Hi. I've used OpenWrt on my Linksys EA7500 v2 for a couple of months, and everything has been working great. I have three separate wifi networks, one of which is for my work computers only and the other two are for the rest of my stuff at home.

Everything worked great until last week, when we changed ISP. After that I'm suddenly getting intermittent connectivity issues to Google sites like google.com, 8.8.8.8 (DNS) or other stuff hosted at Google. The weird thing is that this is only happening for my work wireless network, not the other ones and that that the problems are only for traffic to Google sites (as far as I can see). The rest of the internet works fine.

Things that I have tested:

  1. Resetting the interface for my work network makes the Google connectivity work again for a couple of seconds or minutes, but then it stops working again.

  2. tcpdump from within Openwrt SSH - looks like the packets are flowing just fine (I think) when I'm doing failed ping attempts from my Windows laptop:
    20:53:46.291684 IP 192.168.20.128 > 8.8.8.8: ICMP echo request, id 1, seq 24286, length 40
    20:53:46.293148 IP 8.8.8.8 > 192.168.20.128: ICMP echo reply, id 1, seq 24286, length 40
    20:53:51.060835 IP 192.168.20.128 > 8.8.8.8: ICMP echo request, id 1, seq 24287, length 40
    20:53:51.062294 IP 8.8.8.8 > 192.168.20.128: ICMP echo reply, id 1, seq 24287, length 40
    20:53:56.075609 IP 192.168.20.128 > 8.8.8.8: ICMP echo request, id 1, seq 24288, length 40
    20:53:56.076999 IP 8.8.8.8 > 192.168.20.128: ICMP echo reply, id 1, seq 24288, length 40
    20:54:01.073684 IP 192.168.20.128 > 8.8.8.8: ICMP echo request, id 1, seq 24289, length 40
    20:54:01.075171 IP 8.8.8.8 > 192.168.20.128: ICMP echo reply, id 1, seq 24289, length 40

  3. Tried creating a new interface and a corresponding wireless network for it from scratch, leaving all the default settings - Still the same result (plus I'm getting some stability problems getting my wireless networks working now, but that's for another thread).

Any ideas on what to try next? Let me know which configs you'd like screenshots or files for.