I've played this game a lot of hours and not changed anything recently. I last played a couple of days ago with no problem. Today, when I started the game, I immediately (on the various splash screens and the main menu screen) noticed my mouse cursor was rapidly migrating across the screen to my left. This made it impossible to click any of the options on the main menu. When I close the game using Windows Task Manager, the problem stops and doesn't recur until I restart the game. I've never seen this problem with any other app, and I've used this sytem extensively for five years.  I tried rebooting my system to no avail. I tried unplugging and replugging the mouse. I verified my local (Steam) files.

V1.8.2 S3 (64-bit)

OS      Windows 10 Home

CPU Intel Core i7-4790K

FAN CM Hyper 212 EVO

MOBO ASUS Z97 PRO LGA 1150

GPU Gigabyte GeForce GTX 980

RAM Crucial Ballistix 8GB

SSD Crucial MX 200 250GB

HDD Western Digital Blue 1 TB

CASE Corsair Carbide 200R

PSU Corsair CX600

ODD Samsung 24x SATA

Monitor: LG 24GM77

Keyboard: Steelseries Merc Stealth

Mouse: Steelseries Rival 310 eSports

Speakers: Philips SPA 2210

Microphone: Blue Yeti

Ping 34 ms : DL 13.2 Mbps : UL 0.86 Mbps (6/16/2020)

Firestrike 1.1 score = 11,588 (graphics = 13,883; physics = 11,748; combined = 5127)

Here's more weirdness for you: I restarted the game after the computer had been asleep for about three hours and the mouse is working fine. Go figure!