Why does my external USB drive keep disconnecting and reconnecting on Windows 11?

Why does my external USB drive keep disconnecting and reconnecting on Windows 11, sometimes every few minutes, and sometimes only when I'm transferring large files? I hear the disconnect sound, the drive vanishes from File Explorer, then it reappears a few seconds later. It's happened with multiple drives and multiple ports, so I don't think it's the cable or the enclosure. I've already disabled USB selective suspend, turned off power saving for the USB hubs in Device Manager, and checked for updates, but it still happens.

Is this a power management issue, a driver conflict, or something in Windows 11 that's putting the USB controller to sleep? And is there a way to keep external drives connected reliably without disabling sleep entirely?