I'm prepared to bet you are using a laptop with a touchpad. If so, when
typing the heel of your thumb brushes the touchpad and moves the insertion
point. Most of the time you aren't even aware of it.
Frankly it's a bloody nuisance, and you aren't alone in having this problem.
The touchpad driver may have a way of reducing its sensitivity.
If I'm off-base about you using a laptop, please accept my apologies!
SteveT