In the last week I have had all my presence sensors and 2 ZigBee switched go HUB_DISCONNECTED in the IDE. They still operate fine but the red dot is annoying 
Old posts indicate power cycling and “waiting” doesn’t help, anything else to try?
reboot the hub from the IDE.
That did it, thanks!
Didn’t try the hard boot as other said it made no diff.
I have multiple devices that show OFFLINE in the Smartthings app/IDE, they cannot be controlled by the Smartthings app and will not go online when the hub is rebooted. At first it was one device, then two, then three and now over time several. Weird thing is while I can’t control them via Smartthings they can still be controlled by Google, Alexa and Webcore. What gives? Do I need a new hub? I have even tried cutting the power to an offline outlet for over an hour (all Jasco) and that didn’t work. Removing and reading to the hub doesn’t work. At first it was only my Jasco outlets and now my first and newer Jasco dimmer switch.
Do you have Device Health on in the app? I discovered that switching it off my devices came back on in the app although it was still being reported as HUB_DISCONNECTED in IDE.
Just had the same situation and the IDE - hub reboot did the trick. Thanks for sharing.