We could fix it for the adress-book and calendar buttons (but not for "new mail") by adding this CSS:

/ iOS/WebKit Rendering Fix for Angular-Material FAB in SOGo /
@supports (-webkit-touch-callout: none) {

/ Action items and buttons get their own compositing layer /
md-fab-speed-dial .md-fab-action-item,
md-fab-speed-dial .md-fab-action-item > button {
will-change: transform, opacity;
-webkit-transform: translateZ(0);
transform: translateZ(0);
-webkit-backface-visibility: hidden;
backface-visibility: hidden;
}

/ When fab is open, force visible final state (Safari sometimes keeps scale(0)) /
md-fab-speed-dial.md-is-open .md-fab-action-item {
opacity: 1 !important;
-webkit-transform: scale(1) translateZ(0) !important;
transform: scale(1) translateZ(0) !important;
}

/ If taps don't register, ensure pointer events are enabled /
md-fab-speed-dial.md-is-open .md-fab-action-item > button {
pointer-events: auto !important;
}
}