How to fix blank thumbnails in the WordPress Media Library

Soution 1:

 Disable all of your plugins and test to see your media library is working.

 

Soution 2:

Step 1: Login your admin panel.

Step 2: Go to Settings > Media

Step 4: Than Click (Organize my uploads into month- and year-based folders) option Check box 

Step 5: Than Click Save Change  Button