Just had a ADS/Sprint bug and I think its related to shotgun.
I took up the shotgun, reloaded and shot again. After that I could only ADS and sprint with shotgun, not the UMP or pistol. Tried changing weapon slots, didnt help.

If I hold ADS while using shotgun and scrolling to UMP while still holding ADS, ADS worked for both pistol and UMP. Sprinting only worked with shotgun however.