If the user has an external hard drive with many, many image and video files and folder, connected to the computer, Windows 10 and Windows 8 may detect it as a Portable Device (Windows 7 and earlier would not). This causes the import dialog to treat it as if it was a camera, or card reader, and therefore will iterate through the device discovering all the image/media files it may contain.

The real problem appears when an end user is using a large external hard drive as a means to back up a significant amount of data. In that case, ACDSee will take an extremely long time to iterate through all that data, discovering which images/videos it should show in the import dialog. On Windows 7 and earlier, external drives were never considered portable devices by the OS and thus never displayed any data in the import dialog.
Workaround:

The workaround is to disable the Portable Device function of the device in the hardware properties of the device in Windows:

-    Desktop mode, go to Control Panel | Hardware and then Sound | Devices and Printers
-    Right click on the removable drive and then click Properties.
-    In the Hardware tab of the Properties dialog, look for an entry in the Device Functions List which has the type
     Portable Device. Select this row, and click Properties
-    In this next Properties dialog, click 'Change Settings' and then go to the Driver tab and press the Disable
     button, and press OK in the confirmation dialog.

This will disable the Portable Devices behavior for the offending external drive. The device should still mount correctly as a Mass Storage Device and should continue to appear in Windows Explorer