Answer by George Siggouroglou for Prevent BODY from scrolling when a modal is opened

The above occurs when you use a modal inside another modal. When I open a modal inside another modal, the closing of the latter removes the class modal-open from the body. The fix of the issue depends on how you close the latter modal.

If you close the modal with html like,

<button type="button" class="btn" data-dismiss="modal">Close</button>

Then you have to add a listener like this,

$(modalSelector).on("hidden.bs.modal", function (event) {
    event.stopPropagation();
    $("body").addClass("modal-open");
    return false;
});

If you close the modal using javascript like,

$(modalSelector).modal("hide");

Then you have to run the command some time after like this,

setInterval(function(){$("body").addClass("modal-open");}, 300);