Following the most recent Windows 10 update, JRiver Media Center 27 would lock up after an hour or two of successful playback on the external-USB-hard-drive-equipped laptops that serve as program sources for my standalone bedroom (Dell early-generation i7) and living-room (HP AMD A12) audio systems. Clicking on a media file (WAV, FLAC, up to DSD 128 and PCM up to 24/352) on the laptop's external hard drive would stall out operation, with the only sign of life on the monitor a spinning blue circle signifying "I'm going nowhere." Often at that point, the USB drive would disappear from the list of active computer drives.
I deleted and reinstalled the USB drivers, cold-booted or restarted the affected computer, and usually got back up and running for another hour-or-two music playback session before the problem reappeared. Significantly, it did not affect a third, much older computer, an HP desktop that, via an external USB drive as source, feeds music to my home-office system. It, too, had the latest Windows 10 update.
After a couple of days of hair-pulling, I remembered seeing somewhere that USB and Bluetooth may at times not play well together. So I checked the settings of both laptops, discovered that there was a Bluetooth setting for each, and its default was "ON" in both cases. I turned that setting "OFF." The older, and problem-free, desktop had no Bluetooth setting.
I've now had both laptops playing music via MC27 for several hours with no lockups and no problem seeing either external USB drive. Keeping my fingers crossed.
Posted here as an FYI in case anyone else has a similar problem.