When debugging issues it is often useful to see what errors are being generated by WordPress. Normally, these errors are not logged anywhere. However, a log can be generated by turning on WordPress debug flags in the WP-CONFIG.php.
The WP-CONFIG.PHP file is located in the root folder of your WordPress install and can usually be accessed and updated with any FTP client such as Filezilla.
Once you have the file open, you need to add the following items in it:
define( 'WP_DEBUG', true ); define( 'WP_DEBUG_DISPLAY', false ); define( 'WP_DEBUG_LOG', true );
It is important that you place these entries anywhere ABOVE the line with the words /* That's all, stop editing! Happy blogging. */
Save the updated file back to your server. Once saved, the error messages will be written out to a text file called debug.log.
The debug.log file will usually be generated in the wp-content folder. However, some hosts will move the file to a more secure location - in which case you will need to contact them to access it. The file will not be generated until an error occurs.
You should try whatever actions is causing you an issue and then see if this file contains new data in it. You can also delete the file completely before trying your operation - it will usually be generated again when an error or notice occurs (unless the host has remove file creation privileges for the webserver user account.
Read more about debugging in WordPress:
Using the WordPress debug log (Elegant Themes)
Debugging in WordPress (wordpress.org)