Why won't my 950xl stay on vibrate ?

[JB6464]

I always keep my 950xl on vibrate for all receiving calls but every time i make or receive a call it resets itself to the low volume setting and i miss my calls so i have to pull down the notification window down and reset it to vibrate again .
I also have the phone set on vibrate in the personalization / sound settings in the phone but the above issue keeps happening .
Anyone have this issue or know how to solve this problem ?

 

[MohamedWaheed]

No, I don't have this issue with my Lumia 950XL.
Are you using an insider build?

 

[JB6464]

Bought this phone new from Microsoft local store two weeks ago , not sure on the insider build . How do i check if my phone has that build in it ?