I have reported similar issues to Smartthings support a year ago. They have blamed my network setup as my Hub is connected to a wireless AP.
This was their answer:
“SmartThings has been designed to run directly plugged into a router and not purposely built to be used with a switch. With that said, we do have known users who have the Hub connected to a switch and works fine for them. However, this may vary from user to user as we have found there to be stability issues for others. It will be great if you could give it a test and monitor for a period of time by plugging your Hub directly to the router to see how everything works for you.”
Hub disconnects and reconnects are carried along since. Recently increased a lot. I can see on the Hub’s LED that it goes blue and turns green again.
A year ago the issue was that bad, as looking at the events log of the hub for the 3 days I could see 1417 hubStatus messages (disconnected and active), and 626 register messages.
I haven’t looked at the logs recently, but there is still no option to filter the messages (I asked for that feature a year ago though), and all of it is spammed with the ssdpTerm messages from local network discovery, so cannot really see the disconnects when it has happened more than a few hours ago. The browser fulfills the memory of the computer when trying to load more logs due to the wrong design of the ide page, bummer.
Meanwhile I have another reported bug for a year too, when a camera tries to make a still image the transfer of the image brakes and reboots the hub.
Maybe that is a main feature of the hub that it reboots/disconnects randomly and continuously.