Starting with macOS 10.13 High Sierra or possibly earlier, the system process VDCAssistant has tended to lock up the Leap Motion controller. You'll thus see it among your USB devices but the Leap Motion daemon cannot talk to it during this period.
Often it eventually times out after a couple minutes and leapd gets ahold, but there is no guaranteed wait time and this can certainly be frustrating.
One workaround is to pause VDCAssistant with the command:
sudo killall -SIGSTOP VDCAssistant
and then plug in your Leap Motion controller. Please try that out and see if it at least gets more information to appear in the log.
Note that you won't be able to use your built-in webcam while VDCAssistant is paused. To resume when done using your Leap, run the same command except with