Can Invisalign Cause Hollow Cheeks?

Although "never say never" and "anything is possible", often the results are the opposite.  Many times expansion of arches are necessary, which results in a more full face.
The treating Dr should be able to help educate you on what to expect.

I have yet to see a case where a patient ended up with hollow cheeks from Invisalign Treatment.  In fact, the opposite is usually true since Invisalign expands/broadens the arches -- it may result in fuller lips or cheeks.

Invisalign will usuall do the opposite. It expands or widens the arch for most patients, which is the most common problem we see. I suppose someone with a very broad upper arch with gaps between all their teeth who used Invisalign to close the gaps could see a slight narrowing of the arch but usually not enough to see with the naked eye.
PS: You Tube is not the place to go to get information about a specific treatment for yourself. One person's case will not be the same on you.