When Overwatch hero ​Brigitte gives Sombra a Repair Pack while Sombra is hacking, it will break the hack and put the ability on cooldown, just as if she took damage from an enemy. 

After her recent changes, including no​ longer gaining ultimate charge from health pack healing, her ultimate comes up far less than it used to, and now having to worry about ​well-meaning Brigittes on your team interrupting that and putting your ultimate on cooldown means bad news for Sombra mains.

Chances are this is not an intentional part of the game and is ​merely a bug that needs to be fixed. 

Photos courtesy of Blizzard