Providing more information about system specs wouldn't hurt anything. But from the evidence I've seen, most if not all of these performance issues are directly tied to network/netcode/server issues.
The game's netcode (client and server side) does not handle network interruptions well. Furthermore, I've seen evidence that the game's render loop is bound to the netcode, blocking until all requests/responses are resolved before rendering frames. I've black box tested this (and other possible causes of these issues) using the game's resource meter, Wireshark, Window's Resource Monitor and various cpu/gpu monitoring tools.
Using the game's resource meter, you can observe the game's framerate is directly tied to the network latency between the client and server. When the latency rises, the framerate drops in lock.
Using Wireshark, you can observe all of the network traffic going to/from the server gateway. Nearly all client-side actions, including those that do ...