iOS position: fixed glitches

I’m facing a glitch in iOS where position: fixed elements display behind other elements.

css:

.__header {
    position: fixed;
    top: 0;
    background: #000;
    height: 40px;
    width: 100%;
    z-index: 100;
    display: flex;
    justify-content: center;
    align-items: center;
}

    .footer__menu {
        width: 100vw; 
        height: 70px; 
        position: fixed; 
        top: 0;
        z-index: 199;
        background: #000000;
    }

Everything works great in android and chrome.