Ballistic switches back to sling gun after i switch to main guns by itself.

Been happening a ton lately when playing Ballistic. I'm not sure if it's specific to Sling Devotion or the secondary gun. But in the attachment video you can see at around 3th second mark I switch to my secondary gun R99 and immediately after it switches back to the Sling gun which I just used and switched from. Died lots of times because of this issue.