Hello,
Between 4:00 pm UTC (4/21) and 7:00 pm UTC (4/21), we will be automatically updating your Hub to the latest firmware. The update is expected to take less than 10 minutes, during which time your Hub will temporarily go offline.
The firmware update includes a fix to address some Hubs staying offline until a reboot, improvements to ZigBee device pairing, improvements to LAN-based device connectivity, and fixes to address issues with SmartApp execution when using a large number of devices.
Thank you,
SmartThings Support