Drag and drop won't move ALL selected files between Finder windows
Solution 1:
I know this is late but I've found a fix.
First, open disk utility and run first aid on your disk.
Second, shutdown the computer fully and disconnect all USB devices.
Third, Press the power button and hold command-option-p-r until the Mac reboots again. This will reset the PRAM.
I hope this fixes your issue like it did for me!
Solution 2:
I found solution, in System Preferences -> Accessibility
