I changed it with a new RSHTech 7-port USB hub, and the black-screen reboots continue. I'm stumped at this moment, really beginning to suspect my UPS of spikes or momentary cutouts. Anyway I think the Sabrent is https://deborahvhmd490889.jts-blog.com/27975087/iogear-2x4-usb-3-1-gen-1-type-a-peripheral-sharing-switch-fundamentals-explained