No, clip-in hair extensions are not capable of causing bald spots or hair loss.
The typical process for hair growth is when the follicle produces normal strands of hair that grow out over a couple of years, then shed to produce new growth. When a hair follicle is affected, however, it shrinks and becomes smaller in size, and produces hair that is finer than normal. While new hair typically stays put for a couple of years before shedding, affected hair follicles shed much quicker and grows out much slower. As a result, the follicle is not able to continue the proper hair growth life cycle, resulting in balding.
If you are experiencing balding or excessive hair loss, we recommend to consult with your doctor.