I am having the same problem as the others, I have to unplug the usb connector from the charging plug and reinsert it for the device to power on. Once on, the device works correctly. If I power off the tv, the device also goes into sleep mode. If I wait a minute or two and then power on the tv, the device will usually work as well. If I wait for a period of time or over night, the device will not come up when I start the tv. I have to unplug the usb connector and reinsert it for the device to work,.
I have two other express 4k+, and they are working correctly. It is only this one that is giving me a problem. If I have to hazard a guess, this device is faulty. I even went so far as to unlink it and reinstall it, but this did not help.