It has stick drift

In my experience, stick drift is generally a factor of one thing—analog joysticks. They tend to develop this problem across the board as a side effect of the way they function.

iFixit has a few resources that detail this issue and if you want some more in depth explanation I would check out this page on Hall Effect Joysticks which goes over the limitations of more traditional analog type sticks. Even though superior technologies exist, they still appear in the vast majority of gaming controllers.

Essentially, your solution here will probably be one of 3 things.

1. Clean the joystick mechanism since grime in some parts can result in incorrect readings.
2. Replace the joystick itself, which could have wear in some spots, causing readings to be incorrect.
3. Replace the the whole controller. Replacing the joysticks will require soldering skills and having someone else do this repair if you're not capable will likely cost more than replacing the whole controller. There isn't a joystick replacement guide for this controller, at least not at iFixit, but you can reference the guide for the stock Xbox controller to get an idea of what's required.