Try setting Preferences / Miscellaneous / Advanced [Filesystem]: copy_buffer_size to 60 KB. Some USB devices have problems with larger buffer sizes, and that might be causing it to disconnect all the time. (If it doesn't help, reset it back, since it can affect copy performance.)
Opus only calls high-level APIs like CreateFile, ReadFile and WriteFile, so if the drive keeps disconnecting it's going to be a fault in the drive or USB device/driver it's connected through. There's nothing in Opus that would disconnect a drive, short of the Eject command being run. But we have seen USB devices that don't work properly with larger buffer sizes (as well as ones that don't work with non-buffered I/O, but that's off by default and you'd know if you had turned it on), where the devices were apparently only ever tested against the buffer sizes Explorer uses.
I would also check in Event Viewer under Windows Logs > Application and Windows Logs > System. There may be Error or Warning events in there coinciding with the times of the disconnections, which could give more detail on when or why the disk is disconnecting.
If you can capture one of the disconnects with Process Monitor we could look at that to see if it reveals something as well. A similar log of what Explorer does with the drive could also be useful for comparison (that would tell us the buffer size Explorer is using, for example; it varies by device and connection type).