How can I pinpoint the cause of brief, random internet dropouts?

It would also be worth checking the router models and running a bufferbloat test, even if nobody else is actively using the connection. Bufferbloat usually appears when the connection is busy, but router firmware or traffic-management problems can still cause brief interruptions. Since the connections are rated at 1 Gbps and 2 Gbps and both use ISP-provided equipment, check for firmware updates, event logs, overheating, and whether the equipment is acting as a modem, router, or both. During an outage, compare the router’s status page with the ping results; that can show whether the WAN link itself is dropping or only the computer’s path to the internet is affected.

Wireshark is free and can capture network traffic, but it may be more detail than you need for a short dropout. A simpler approach is to run several continuous pings at the same time: one to the local router or gateway, one to a public IP such as 1.1.1.1, and one to a hostname such as example.com. If the gateway stops responding, the issue is likely local. If the gateway responds but the public IP does not, the modem, router, or ISP link is more suspicious. If the IP works but the hostname fails, look at DNS. Save the results with timestamps so you can compare them when the next interruption happens.