Constant DNS Timeouts (Showing as Connected Without Internet)

[LookMum_NoHands]

Starting to lose my sanity here.
Problem really started in mid 2022 when my elderly Hub 3 started playing up with DNS timeouts. VM replaced with a Hub 5 and all was fine until this summer when an electrical storm groundstrike about half a mile away upset the Hub 5. 

This presented as constant DNS timeouts, to a point where the service was unusable. Took nearly a week to get an engineer out, who diagnosed a blown line noise suppressor thing (in the wall box) and a dead hub. Hub replaced, everything groovy until this week when the DNS timeouts started again. Did a pinhole reset and the hub had a total meltdown and wouldn't accept the Settings Password. 

Engineer out day before yesterday - apparently the signal is fine, but Hub is not. Replaced Hub, everything back to normal... for a grand total of 24hrs... and it's back again.

Setup:
350mb/s service on coax, Hub 5. Custom SSID, 2.4ghz only, signal switching disabled. 
TP-Link 108 switch for the wired connections in the house, with a pair of TP-Link EAP 115s (upstairs, detached garage). Running in as basic a mode as possible, same SSID as the Hub. 

Symptoms:
Mobile devices report 'Connected Without Internet' in their Wireless settings screen. Condition exists for 3-15 seconds before reverting to 'Connected'. Device will flick between the two states endlessly.
Wireless Laptop will demonstrate same issue, takes much longer to recognise the internet is there.
**note, this occurs on wireless connections to the hub and the two EAPs - I've spent a lot of time disabling things, switching signal, etc etc. 
Wired connections (Stream TV box, gaming PC, PS5) also have the same problem, but it tends to be on start up where device will take minutes to recognise it has an internet connection. 

Investigations/RCA
Speedtest from any device will consistently report either 300mb/s+ or 24mb/s... there's almost nothing in between. 
Broadbandchecker - everything fine. Latency within normal, very occasional packet loss spike once or twice a day. 
Ping both primary and secondary DNS servers - absolutely fine
Ping 8.8.8.8 - absolutely fine

Before I spend another ridiculous amount of time arguing with offshore 1st line about turning the flipping thing off and on again - Anyone got any clues what to check/test/hit next?

Note - I worked for VMB for 7 years, and have spent a lifetime in IT infrastructure sales (so I know just enough to get by).  

[Client62]

Connected but no internet access are the symptoms of a Hub 5 in Router mode with DHCP failure.

Checking the network configuration of the failing devices it may reveal the :-
1) IP is not in the 192.168.0.xxx range
2) Gateway is not 192.168.0.1

Either situation will result in a device that fails to reach the internet.

[LookMum_NoHands]

Thanks Client62

Just checked my mobile phone (connection dropping in and out whilst doing it)

IP is 192.168.0.171

Gateway I can't remember how to find that on the phone 
Checked DHCP settings on the hub

Starting local address is 192.168.0.10

Also, the Hub is less than 48hrs old!

[LookMum_NoHands]

Pretty certain it's not DHCP failure - the IP addresses aren't changing, from the Hub control panel I can see everything that's currently polling on the LAN/WLAN. 

Example behaviour, which is why I'm still thinking it's DNS timeouts:
On phone, open YouTube App.
App launches, loads headers but not thumbnails.
WiFi icon shows traffic, then exclamation mark, then the Geo Pin icon flashes (so phone has swapped to 4G), then WiFi returns. 
Thumbnails should load at this point. Press a video, page loads, and then everything pauses as we go through the same thing again. 
Video will then play, but comments won't load initially. Throughout the video it'll be exhibiting the same behaviour with the WiFi and Geo Pin icons. 

This is happening on 2 x Samsung S10s, a Galaxy Tab, and a current gen iPhone.

Windows Laptop and Macbook Air have similar issues, but seem more stable - presumably because they wait longer for DNS timeouts. 

Additionally, everything is talking East-West normally. If I turn the printer on, that communicates across the network fine. I can RDP into the Gaming PC from the laptop without any issues. It's just the internet that's failing

[Kath_P]

Hi LookMum_NoHands, 

Thanks for taking the time to contact us via the Community. It's lovely having you on board with us in the Forums. ⭐

We're sorry to hear you're having an issue with your broadband service. Taking a look at things this end, your downstream power levels are too high. We won't be able to fix this remotely so I would like to arrange for an engineer to come to take a look at this for you. 

I just need to confirm the address to ensure we are booking the visit on the correct account. I have sent you a direct message to allow us to do this with you in a private space. If you are using a PC/Laptop then you can just click on the little ✉ at the top right-hand side of the page to access your inbox. If you are on a mobile/tablet device then instead click on the little circle icon in the top right then select 'Messages'. 😊

Thanks,