All the other server certificates and SSL keys are good . However, there may be some specific server certificates and key files are not displayed under SSL files in NetScaler GUI .

The same server certificates and SSL keys exists under /nsconfig/ssl.

When we use vi to edit the server certificates or key files, we can see Windows newline charactor ^M at the end of each line. It is by-design that the server certificates and key files can't be displayed in GUI when they are ended with Windows newline charactor. 

^M means Windows newline charactor \r\n. We need to replace it with Linux newline charactor \n .

shell
cd /nsconfig/ssl
vi <cert_file_name> => confirm ^M is there at every line. Exit vi 
perl -pi -e 's/\r\n/\n/' <cert_file_name> 
vi <cert_file_name> => confirm ^M is gone. Save the change and and exit vi 

After this change, you can refresh the GUI to verify whether the certificate can be displayed.

Note: Please backup your previous certificates and key files before the operation.

 This article describes a situation where some server certificates and key files are not displayed under SSL files in NetScaler GUI