The Sony Xperia Z1 Compact (D5503) has seen a new firmware update certified by the PTCRB in the form of build number 14.3.E.0.1. This build template differs from previous firmware which moves from 14.3.A.0.XXX to 14.3.E.0.X. In the past, a different letter in the build number has suggested it could be a firmware build for a particular carrier.
We expect Sony to fix the notification sound issue in the next update, along with the problem that some people are having waking their Xperia Z1 Compact. Whether or not these fixes turn up in this latest certified release, we’ll have to wait and see.
Thanks czekker Razvan_XP and @SirRobin78!