BBBlack boots with uart not running

I have a python script that successfully configures the ttyO1 uart1 using the device overlay from armhf website for the uart1.
That script is configured to start on bootup of the bbblack but sometimes the uart1 gets configured and works all fine but sometimes not. Why is that?
I have carefully given all the needed permissions to all the related files!
I'm using ubuntu image from robert c nelson