topic Re: Significant Speed Drop - Only Fast When Using VPN (Possible Throttling?) in Network

Significant Speed Drop - Only Fast When Using VPN (Possible Throttling?)

djs88 — Thu, 08 Jan 2026 09:52:24 GMT

Over the last 3-4 weeks I’ve seen a dramatic drop in speeds on my Three connection, going from around 120 Mbps down to 5-15 Mbps.

What’s particularly interesting (and concerning) is that if I run the same speed tests via my work VPN (Cloudflare Zero Trust), I immediately get full speeds again (120 Mbps). As soon as I disconnect the VPN, speeds drop straight back to 5-15 Mbps. This is consistent across Speedtest.net, Fast.com and Cloudflare’s own speed test.

This strongly suggests traffic shaping or throttling is being applied to normal traffic, but not to encrypted VPN traffic.

I contacted support and was told that because I’m using a phone SIM in a router (NX500), it’s subject to different traffic/bandwidth management and that I “need a data SIM” instead. However, when I took out the contract I was explicitly advised there was no difference between phone and data SIMs for data usage, and the connection performed perfectly until a few weeks ago.

So nothing has changed on my side:

Same SIM (3Internet APN)
Same router (NX500)
Same location (100m from mast)

Yet performance has dropped significantly unless traffic is hidden behind a VPN.

Can Three please clarify:

What has changed in the last few weeks regarding traffic management?
Whether phone SIMs are now being actively deprioritised when used in routers?

Any transparency would be appreciated, as at the moment the only way to get usable speeds is to tunnel all traffic through a VPN.

Re: Significant Speed Drop - Only Fast When Using VPN (Possible Throttling?)

djs88 — Mon, 12 Jan 2026 14:32:42 GMT

Speedtest results below, first entry is without VPN connected, second is with VPN connected:

Re: Significant Speed Drop - Only Fast When Using VPN (Possible Throttling?)

Bodger123 — Sun, 18 Jan 2026 21:55:27 GMT

Please let me know if you get anywhere with support. I have the exact same issue. When I connect to my office with a VPN I get full speeds, connected to the internet I'm lucky to get 13.4Mbps down!

Re: Significant Speed Drop - Only Fast When Using VPN (Possible Throttling?)

djs88 — Mon, 19 Jan 2026 09:40:26 GMT

I haven't got anywhere yet, they have just told me it's down to congestion on the mast - which is very likely a way of them saying they don't have a clue and just to deal with it.