Why is my Notification bar lagging in Oneplus One?

[AC Question]

Why is my Notification bar lagging in Oneplus One

I have been using Oneplus one since 4 to 5 months. I am having a lag issue, when I pull down my notification bar down , it lags .
I have tried all my tricks , like factory reset , cache clean , boosting apps but no effect.
My OS is 5.1.1 and CM 12.1
Not rooted .
Plz help me which I can do without rooting my phone

 

[Jack Brown7]

Do you have any apps installed that could be trying to send notifications?