Event Code 4625 in Windows logs indicates a failed logon attempt. This could be a sign of someone trying to guess the credentials of a valid user account by repeatedly trying different passwords or usernames. This is known as a brute force attack and can be used to gain unauthorized access to a system or network. References:
https://www.cisco.com/c/en/us/td/docs/security/ise/2-4/admin_guide/b_ise_admin_guide_24/b_ise_admin_guide