The Sony Xperia T3 (D5103) has seen a minor firmware update released, moving the build number from 18.1.A.1.21 to 18.1.A.1.23. The update has only arrived on a select few carriers in Europe (see details below). This bug-fix update mends some of the reboot and GSM connection issues that some users were facing. It’s unclear at this stage whether this firmware will see a wider release.
Via XDA.