Router can ping DuckDuckGo, PC and iOS devices can't

[XIII]

Weird problem tonight; I'm suddenly unable to access the search engine DuckDuckGo on my PC and iOS devices.

Even a ping fails:

>ping duckduckgo.com

Pinging duckduckgo.com [46.51.197.89] with 32 bytes of data:
General failure.
General failure.
General failure.
General failure.

While on my router ping works fine:

# ping duckduckgo.com
PING duckduckgo.com (54.229.105.203): 56 data bytes
64 bytes from 54.229.105.203: seq=0 ttl=51 time=26.501 ms
64 bytes from 54.229.105.203: seq=1 ttl=51 time=28.305 ms
64 bytes from 54.229.105.203: seq=2 ttl=51 time=28.514 ms

Notice the different IP addresses while DNS is obtained from my router.

On my PC:

>nslookup duckduckgo.com
Server:  router.asus.com
Address:  192.168.1.1

Non-authoritative answer:
Name:  duckduckgo.com
Addresses:  176.34.135.167
  54.229.105.92
  176.34.131.233
  54.229.105.203
  46.51.197.89
  176.34.155.20

On my router:

# nslookup duckduckgo.com
Server:  127.0.0.1
Address 1: 127.0.0.1 localhost.localdomain

Name:  duckduckgo.com
Address 1: 176.34.155.20 ec2-176-34-155-20.eu-west-1.compute.amazonaws.com
Address 2: 176.34.135.167 ec2-176-34-135-167.eu-west-1.compute.amazonaws.com
Address 3: 54.229.105.92 ec2-54-229-105-92.eu-west-1.compute.amazonaws.com
Address 4: 176.34.131.233 ec2-176-34-131-233.eu-west-1.compute.amazonaws.com
Address 5: 54.229.105.203 ec2-54-229-105-203.eu-west-1.compute.amazonaws.com
Address 6: 46.51.197.89 ec2-46-51-197-89.eu-west-1.compute.amazonaws.com

If I disable WiFi on my iPhone I can reach DuckDuckGo.

If I use Google DNS 8.8.8.8 I still cannot reach DuckDuckGo on my iOS devices via my router.

What's wrong? How can I fix it?

 

[XIII]

There should not be any relation at all (just a weird coincidence?), but at the moment I allowed my PC to reboot to install Windows updates I was able to access DDG on my iOS devices...