You have to bear in mind that Freelancer is a very client-based netcode, stuff like how smooth your mouse is moving is not affected by your connection to the server. There's no communication involved when you move your mouse in the UI.
How up-to-date is your PC? I can only think it's still caused by hardware - I don't believe anything else on the server has changed recently in terms of connections or the mod content itself that could introduce this issue.
Disable any overlays (Steam, GeForce Experience, etc) and settings that may be influencing your input as advised by @Save My Soul. I've had similar issues with GeForce Experience overlays a few years ago until it was disabled.
Please observe your resource monitor as well when it happens.
![[Image: Ramkerawr.gif]](https://sig.grumpybumpers.com/host/Ramkerawr.gif)