This happens when the full width header text is aligned at the bottom.

/* -- START Fix fullwidth header scrolldown overlapping -- */
.et_pb_fullwidth_header .et_pb_fullwidth_header_container.left .header-content {
    padding-bottom: 50px;
}
/* -- END Fix fullwidth header scrolldown overlapping -- */Code language: CSS (css)

or

/* -- START Fix fullwidth header scrolldown overlaps buttons -- */
@media only screen and (min-width: 981px) {
.et_pb_fullwidth_header .et_pb_fullwidth_header_scroll {
width: 20% !important;
}
}
/* -- END Fix fullwidth header scrolldown overlaps buttons -- */Code language: CSS (css)