indexed indexes

Problem with indexed indexes in Adobe Acrobat Reader DC
After starting the Reader [Shift] + [Ctrl.] + I click on "Show more options"
Then I choose for searching for: Selected indexes

A signal sounds and a pop-up Security warning appears without text and selection buttons
After a minute, but sometimes also longer, the text with selection buttons appears.
After clicking [allow] I can finally search the indexes.

With preferences, I have included the path to the indexes folder "D: \ pdf files adobe acrobat \ indexed documents" of my computer in Sandbox security.

Why is the use of indexed indices so cumbersome?
Why do I get a warning regarding the indexes on my computer?
Why does it take so long before I can respond to the warning?

How can I prevent and / or solve these problems?