People Think I’m Stupid

It’s been a reoccurring theme in my life where people around me initially think I’m stupid, but later say “oh hey, you’re actually pretty smart”. At the moment, my coworkers think I’m incompetent and unintelligent even though my performance has been pretty good and I complete projects faster than they do. They constantly talk over me and undermine my accomplishments or give weird reasons as to why I’m surpassing their expectations.

I’m confused why this happens so often and does this happen to any of you?

Edit: I work in tech