I fixed the above Masonry 3-column problem for the Taste theme in Chrome and Safari on desktop with this url for the time being till you fix:
@media screen and (min-width: 1024px) {
div.l-masonry.l-masonry--3 {
display: flex;
}
}
@media screen and (max-width: 1023px) {
.l-masonry--3 {
-webkit-column-count: 1;
-moz-column-count:1;
column-count:1;
}
}