Changes since v4.4.12 (last non-beta release version) are as follows.
Added non-offloaded DPI support - DPI now functions when hardware offloading is disabled, so co-exists with features that disable or bypass it (smart queues, IDS/IPS). This does not change anything when hardware offload is enabled.
GeoIP fixes - all known problems with it resolved, added back end for directional control.
SNMP persistent directory relocated to RAM disk, which prevents "Unhandled kernel unaligned access" crash
Removed core handling script that was causing reboots when large core files were generated
Fix IGMP proxy failing to start during boot a few were experiencing.
Fix potential issue of UPnP failing to start during boot.
Change IPS loading of ipset contents to more efficient method to greatly reduce CPU usage after initial bootup and enabling of service.
xl2tpd package upgraded
Other IDS/IPS back end improvements
Fix ubnt-cfgd zombie process issue
Added SNMPv3 back end
Added lock wait to all iptables operations to avoid errors in cases where multiple operations happen simultaneously.
DPI signature update
Add IDS/IPS back end
Fix in informs for IPv6 PD size (was causing PD size to be cleared in controller).
Add support for sending custom events to controller.
Fix DDNS update public IP checking for NATed WANs
Local UI now checks ping to ping.ubnt.com rather than default gateway for Internet connectivity test
Copy 'hostname' and 'mailname' over during upgrades for consistency with other retained files cross-upgrade (from EdgeRouter, generally no functional impact for USG purposes).
Bluetooth back end updates
VLAN hardware offload improvements
DHCP hardware offload problem fixed
LCM (display) firmware update including splash screen, update process improvements.
Upgrade WARNING:If you have GeoIP enabled, disable it first, then upgrade USG, then enable it again. The configuration has changed in a way that limited unstable controller and firmware version combinations could result in an invalid configuration on the new firmware versions. In that circumstance, if the upgrade is performed with GeoIP enabled, the system will have to be reset to factory defaults post-upgrade.
Downgrade WARNING:If you upgrade to any version supporting DPI without offload, disable offload (or enable IDS/IPS) and enable DPI, youcannot downgrade to a version that does not support DPI without offload. Either disable DPI, or enable hardware offload (or disable IDS/IPS), before downgrading. Otherwise you'll have to reset to factory defaults post-downgrade and adopt again.