Intermittent connection issues loading/changing site- secure connection failed/site can't be reached

[EDIflyer]

Is anyone else occasionally getting a 'connection down' error from Chrome (or 'Secure Connection Failed' from Firefox) when changing page - if I hit refresh it works fine. At first I wondered if it was the site I was using but have noticed it on multiple different major websites over the past couple of months and not noticed it from other locations where I don't use Three Broadband so does seem to be related to the router/connection (this is via wired Ethernet too, so not a WiFi problem).  I've tried changing DNS server in case that helps but no difference.

It mainly seems to happen when trying to first load a site or (annoyingly) at checkout when a different site is being loaded as part of the checkout process.  It certainly doesn't happen everytime but does happen with reasonable frequency.  I've also noticed I often get it when trying to pull/push from/to Github too and have to do so a number of times for it to work (browsing the Github website works fine).

I'm using a NR5103E with Firmware Version V1.00(ACBJ.0)b14 - I tried rebooting it but to no effect.

[EDIflyer]

Thanks for the reply, Jonathan. I'm on iD Mobile and I've not noticed it on my phone when on the mobile network, only when connected to my Three Broadband router. I've also not seen it at other locations with my laptop so it does seem to be a router issue. I must confess I don't recall experiencing when I first got Three about 4-5 months ago, I'm not sure if anything changed in the update a couple of months ago? The way it stops happening with the VPN is also really interesting. It's also not Windows-specific as I've got a Pi 4 on the network running Home Assistant and it has been having issues doing updates - I've then realised if I keep just going 'retry' it works, a bit similar when connecting to Github! 

[EDIflyer]

Ah, OK - hadn't spotted your post! Disappointing no reply yet - hopefully someone from Three will take a look soon.

Out of interest, on the ISPReview thread (where I also posted) someone suggested using a VPN - I tried a Wireguard connection I had and it massively improving things, might be worth you trying that too?  They're wondering if Three are undertaking some sort of deep packet inspection that is causing issues.

[tucu]

I posted about this exact same problem here. It's actually worse in Firefox, sometimes Chrome will retry the request automatically. Same router, same version. Couldn't find a solution yet.