Why my sheet-backdrop not properly initialized in mobile layout?

Hi , i realised that during development, when i inspect my page and started it with a desktop
page and then later i changed the toggle the device toolbar to a mobile device, say iPhones,

the sheet modal works ok and the backdrop, grey color will show and it looks like below,

and when i clicked on the grey area ,it closed the pop out sheet.
but if i started it straight from the mobile view, say , in the same inspect console with the same page i did a refresh and then after refresh if i clicked on the same button , the sheet get pop out but the ISSUE is that there are NO backdrop, grey color and i cannot get it close.

can any one offer me some advice please. thanks.

seems that the modal sheet for grey out or something is not working properly.

I have added the following properties to my sheet component, so far it is working for me,

var app = new Framework7({
sheet: {
swipeToClose :true,
closeByBackdropClick : true,
closeByOutsideClick : true,
closeOnEscape : true,
backdrop: true,