The Switch’s and Lite’s analog stick’s are both flawed with how they are manufactured. There is component within the analog stick that wears away and with longer/more use it causes the drift-like issues you are experiencing. Exchanging it with a new Lite will fix it at first, but those issues will likely come back again. This is why there is a free fix (in North America that I know of) for this issue right now because they know that the analogs are flawed. Hopefully Nintendo will address this with an updated/better analog stick.
This video will explain how and why there’s drift.
There are other fixes for this problem, such as electrical contact cleaner, isopropyl alcohol, and even compressed air that will fix the problem temporarily and the steps for those can be found on YouTube.