Why did system suddenly "lock" most of my files?

HELP, PLEASE!

Two days ago a program suddenly ran and "locked" most - 36,000 - of my user-name files. What caused that?

Now when I try to open a file I get message that (I) don't have permission to view it.

Get Info for the file shows:

that the file is unlocked,

"You can read and write."

(Me) Priveledge is read and write.

I've tried:

Get Info: Clicked box for lock and then unlock - still get permission message.

Doing this:

Launch /Applications/Utilities/Terminal and copy & paste this command at the prompt

chflags -R nouchg ~/Documents

Press return.

Result: Selecting all files in Documents and then get info: mixed permissions. Most files in Documents have the permission problem.

Note: many of my files under my user name are not in Documents. Most of these files have the same permission problem.

HOW DO I UNDO THIS PROBLEM?

WHAT MIGHT HAVE CAUSED IT

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MacBook ProCore i7

OS X 10.75

Not using Time Machine

System Preferences - Users & Groups shows me as Admin and current user