Can't sprint with any gun equipped but can with gadgets and equipment.

This fixed it for me:

open steam and go to settings, then click the controller tab and enable "enable steam input for xbox controllers" then scroll down a bit and clickm install on the "xbox extended feature support driver". 

after my PC restarted the issues with not being able to sprint were gone. 

from my research this seems to be an issue with xbox elite controllers but if you have the same issue with a different input perhaps try this fix with your controllers named options instaed of the xbox ones.