Background: I have a Windows 10 desktop set up to act as a dedicated server for a handful of games, with one of the games being Minecraft (Java Edition). My router is set up with a variety of port forwarding rules to allow incoming connections to these various games. The router itself is a Fios-G1100 which doesn't seem to offer a ton of helpful troubleshooting information, but I don't claim to be an expert on all of its available functionality.
Issue: Any computer from within my local network can connect to this Minecraft server without causing issues, but whenever someone connects from outside my local network, my entire local network starts to experience disruptions. This disruption takes many forms, from discord calls being laggy, to online video games disconnecting, but the easiest way to demonstrate this issue is to set up a command prompt to ping google repeatedly. I can tell exactly when someone joins the Minecraft server because a number of my pings start timing out, and continue randomly timing out for as long as they are connected to the server.
Troubleshooting: This issue does not occur when someone connects from outside my local network to other dedicate game servers like L4D2. Switching the ports that Minecraft uses does not seem to change the behavior. Switching from regular port forwarding to DMZ does not change the behavior either. Using a managed switch to port mirror and sniff traffic (using Wireshark) to and from the Minecraft server machine doesn't appear to show any real difference between a local and external connection in terms of the number or size of packets sent and received, although I admittedly don't really know what to look for in such a capture. Since the entire network is affected I would assume that the issue has to relate in some way to my router, but I can't really wrap my head around how that would be the case given the above findings.
Meta: I will likely end up moving the Minecraft server to a paid hosting service to bypass this issue in the short-term, but if possible I'd like to at least understand the underlying cause, and better understand what other steps I can take in my troubleshooting.