Hi @kamalpandey007
I hope you are doing good today.
By default Defender Masking Login protect /wp-admin and /wp-login.php slug. Could you navigate to Defender -> Settings -> Data & Settings and reset settings. After that setup Masking login once again and see if this helps?
Also, is there any other protection/membership plugin on the site which could affect Defender Masking Login feature?
Just to be sure, would you please run a conflict test? Please deactivate all plugins except Defender and check if the problem is gone. If so, then enable all plugins one by one and find which one is having a conflict. If there is no positive result, switch to a default WordPress theme like 2019 and see if it works.
Before this test we recommend full site backup.
Kind Regards,
Kris