This is not a bug but a solution to USB connection problems.
Since I've been interested in astrophotography, I've encountered USB connection problems.
I'm on a Mac (and don't want to use Windows) and I've read in forums that USB connection problems were a "feature" of Apple computers. Why ? Nobody said why.
I've been using several softwares (among them KStars and TheSkyX).
Because these two softwares can manage a lot of devices (scope, dome, cameras, focusers, guiders...), they are also the place where I've encountered USB problems.
Sometimes everything was working perfectly, and sometimes NO device could connect.
On my Mac (MacBook Pro, mid 2014) there are two USB ports, one on each side of the computer.
I used the one on the left side of the computer.
When for some reason no device could connect to KStars, I swapped to the right side USB port ... and everything mounted correctly.
I've been told that a similar situation is found on Windows computers.
Now I'm using only the right side USB port and all devices mount correctly and immediately.
I hope this will help others !

The solution I exposed earlier may not be the best one : checking the USB cables ( replacing them) is probably a better solution !
This is what I did and I found that the faulty cable was a 5m-long USB cable linking a hub (scope + focuser + cameras) to another hub (dome) and then to my computer.
Sometimes the 5m-long USB cable worked perfectly ... and sometimes not and I could not connect the dome, or the focuser or the cameras.
I replaced this faulty cable by two 2m-long USB cables and all devices mount immediately.

I'm adding a last point to this thread : when the hardware doesn't run correctly, a good thing is to restart the machine.
If this doesn't solve the problem, you might try to reset the SMC.
This might be a solution if your computer's fans run at high speed, even though it isn't under heavy usage and is properly ventilated.
On a MacBook, you reset the SMC like this : After your Mac shuts down, press Shift-Control-Option on the left side of the built-in keyboard, then press the power button at the same time. Hold these keys and the power button for 10 seconds.
THIS SOLVED THE PROBLEM FOR ME AND NOW ALL MY DEVICES CONNECT AND MOUNT IMMEDIATELY ON BOTH USB PORTS.