@Echo6Echo I didn't say "server", I said "engine", that is what runs on the client side (Frostbite).
There's rumors that what causes the issue is that the engine is always so "busy" with everything going on in a match that it causes it to "miss" some input signals from the mouse, causing you to overcompensate your aim and the feeling of sluggish mouse movement. That's definitely plausible.
I have a theory that what also could be causing the issue is the heavy implementations of anti-cheat and anti-tamper protections this game has. This game pretty much has no cheaters, which is a very good thing, but it's possible all these layers of protections could be causing issues with how the input is processed. This games uses Denuvo Anti-Tamper and Easy Anti-Cheat on top of that, which together they make the game run in a virtual machine with obfuscated code, all that to protect the game from cheaters. DICE went heavy with these measures in 2042 because of crossplay. This would also explain why they avoid commenting on it.
But then again, this is all speculation! Only DICE knows what causes the issue, or at least I hope they do and fix it once and for all.