Shift key and Drag and drop with mouse

Hey shirazigs,

Thanks for the video. Let's get a little more information to help narrow this down.

Have you tried using a different mouse?

Does this happen if you use the internal trackpad?

Have you tried the mouse on a different computer?

Does the same issue happen if you boot using safe mode? Start up your Mac in safe mode - Apple Support

Keep us posted.

Hi shirazigs,

Thanks for the update. We do suggest trying a different mouse, as well as to test is safe mode to see if the issue persists.

If the issue is present with a different mouse, and in safe mode, you may want to contact Apple Support. They'll be able to look into this with you further: Get Support

Take care.

Hello shirazigs,

Does the issue happen at other times as well, or only when trying to drag and drop content? That information will help us plan how to proceed.

Please check out the information in the following link to ensure the correct process is being used to drag and drop items on your Mac, so we can make sure there any aren't issues there: Drag and drop items on Mac

Drag and drop items on Mac

You can drag and drop items to do things like move or copy files and folders, add an image to an email, or move text around in a document. 

1. On your Mac, select an item you want to drag—such as an image or block of text. 

2. Press and hold the trackpad or mouse while you drag the item to a new location.

To copy the item instead of moving it, press and hold the Option key while you drag.

3. Release the trackpad or mouse to drop the item in the new location.

Thanks!

shift-drag does not have any specific meaning I can recall.

But if your trackpad is a little touchy, and you are still holding shift while dragging, that would make it far easier to lose the selection (or lose a part of the selection) if you got an additional stray click or lost the click.