I’ve got a 20m usb extender, it always worked pretty well with all kind of hardware even with some bandwidth requirements such as the Kinect1 and fullHD cameras. But with UNO/gbrl it looses the usb connection… this is just a statement, I guess I hit the limit of the extender…
Did that happens with the spindle on or off?
Sometimes EMI is to blame (even with short cable runs) if you use a VFD.
At any rate, 20m is way beyond USB spec.
It happens with the spindle off as well. Anyway after writing I ve experienced a grbrl fail even with shor cable. I can recover with ~ just the same as when it happens with rpi/net … this may be due to the bug in gbrl as stated in another post by @jlauer . We are definetely going to switch to tinyg2 this week.
ah also it is a 20m active extender of course