that typically happens if you have configured custom zoom level in browser (different from 100%) or if you have configured some custom DPI in operating system.

• My browser and DPI settings are restored , But I see same issue in IE & Edge browsers ,Chrome is not even getting "Browse" option .
• Also, When i change the css class ".nf-attachmentFileInput "  height property to 30 PX then we are able to fix it. 
• Could you please do let me know how can I permanently fix it

do you customize standard sharepoint's and/or nintex's CSS styles?

or do you apply your custom styles on standard controls along with standard styles?

if so, then I'd suggest to investigate in developer console which style causes this effect.

I am using Custom SharePoint Master Page ,
Is there any possibility to apply global css for all the existing and new nintex Forms 

I would say not, without stepping into each form at least once and configuring reference to your custom style sheet file.

.nf-attachmentFileInput
{
height : 30px !important;
}