After I dropped my lens, focus locks but images are blurry — what could be wrong?

I have a Tamron 24-70 2.8 on a D610. I usually go for small apertures (F11 to 16) since I work with flashes on studio setups, my lens gives sharp images on those appertures but anything below F5.6 starts to get blurred even though AF locks on and MF shows me correct focus on the view finder. It is NOT a misfocusing issue on my part, since I have a Nikon 1.8 and is sharp as a knife at any aperture. Any guesses? I dropped my Tamron knee high but it didn’t hit hard.
I’m kinda lost.