My Wi‑Fi normally reaches around 200 Mbps, but sometimes websites barely load. When I run an internet speed test, the download speed starts high and then gradually falls to about 1 Mbps. If I run the test again, it may begin around 40 Mbps and drop to roughly 4 Mbps almost immediately. Restarting the router only helps occasionally. What could be causing this, and how can I troubleshoot it?
3 Answers
Test the connection over Ethernet first, if your router supports it. If the speed drops the same way over a wired connection, the issue is probably with the 5G modem, cellular signal, or service provider. If Ethernet stays stable while Wi‑Fi falls apart, investigate wireless interference, router placement, or weak signal strength.
This could also be an MTU or packet-fragmentation problem. Try enabling MSS clamping if the router has that option, or temporarily lower the network interface MTU to around 1400 as a test. Some 5G setups work better with an MTU near 1428. If you can, pairing the correct MTU with SQM or smart queue management may also make the connection more stable.
Because 5G home internet uses a shared mobile network, congestion could be the cause. Compare speed tests at different times, especially late at night, and try testing the same connection on a phone using mobile data. Also check the exact router model and move it near a window or another location with better reception. Some 5G routers support external antennas that can be aimed toward the nearest cell tower.
An MTU of 1428 worked well for my own 5G setup after testing different values. With SQM enabled too, the connection became much more consistent while still reaching good speeds.