The short answer

Sudden packet loss almost always has a specific trigger, and the job is figuring out what changed. A connection that worked fine yesterday and is dropping packets today didn’t degrade on its own. Something shifted, either in your home, at your ISP, or on the wider internet, and tracing the cause is mostly about asking what’s different now compared to when it last worked properly.

The good news is that sudden onset loss is usually easier to fix than slow gradual loss, because the trigger is often recent and obvious once you start looking. The bad news is that the trigger isn’t always something you control, so part of the process is ruling out your own setup quickly so you can pursue your ISP if it turns out to be them.

The most common sudden causes

A recent change in your home is the first thing to check. Did you add a new device to the network, move your router, change Wi-Fi channels, install a new app, or update your router’s firmware in the last few days? New devices can saturate older routers. Firmware updates occasionally introduce bugs that get patched a few days later. A neighbour installing a new router on the same Wi-Fi channel as yours can cause interference that wasn’t there before. Think back to the last time the connection was clean and work forward from there.

Background activity is a quiet but common culprit. Cloud backups, system updates, game downloads, and security scans can kick off automatically and saturate your connection in ways that look like packet loss because your router is simply overwhelmed. Check what’s running on every device in your house, not just the one you’re using. A Windows update downloading on a laptop in another room can flatten a small router’s capacity and cause loss on every other device.

ISP-side problems are the next place to look. ISPs do maintenance, suffer equipment failures, and sometimes get hit by issues with their upstream providers. If your loss appeared at a specific time on a specific day and nothing changed in your home, check your ISP’s status page or their social media for outage notices. A traceroute that shows clean hops at home and loss starting at your ISP’s gateway is fairly conclusive evidence that the problem is on their side.

Weather and physical conditions cause more sudden loss than people realise. Heavy rain affects some types of broadband connections, particularly older copper lines and fixed wireless setups. A heatwave can push routers and modems into thermal throttling. A storm can knock equipment offline at exchanges. If your loss appeared at the same time as weather changed, that’s worth noting.

The less obvious triggers

Malware or a compromised device is worth ruling out, especially if the loss appeared after someone in the house installed something new or clicked a suspect link. Malware can saturate a connection from inside, generating traffic that competes with everything else and causes loss. A quick scan with a reputable security tool takes ten minutes and rules it out.

A failing piece of hardware that’s been declining for weeks can also feel sudden when it finally crosses a threshold. A router with a dying power supply or a fraying ethernet cable might work fine for months before tipping into noticeable loss. The fault was building gradually but you only feel it once it crosses the point where you actually notice the symptoms. If nothing else explains the sudden onset, swap suspect cables and try a router reboot. If a reboot fixes the loss temporarily but it comes back within hours, you’re looking at hardware that’s on its way out.

Construction or infrastructure work in your area can cause sudden loss too. New cabinets, repairs to underground cables, or work on nearby exchanges can degrade your line quality without anyone telling you. Your ISP can usually check whether work has been logged in your area if you call them with the timing and ask.

The diagnostic process is the same regardless of which trigger you suspect. Run a ping test, run a traceroute, note the times when loss is worst, and work outwards from your own equipment until you find the hop where loss starts. The cause becomes obvious once you know where in the chain it’s happening.