Account Password is Changed irregularily

Hi All, We have a reset password flow  in our application which is accesible by anonymous session. The reset password fucntionality is only accesible from login Screen for users.  We are facing a irregular issue where As a admin I have resetted the password for few users from the Admin Account. Users are able to login with password which admin has set for them . But after 1-2 days the password is changing automatically. When the user enters the Login name and password it is showing Sign in Failed.  When i checked he logs it says Invalid password. This issue is randomly occuring for 1-2 or 1-4 days, because of this users are udating their pasword daily using set password link. Has any one encountered this kind of issue.  Please acknoweledge me with solutions inorder to solve the issue. Thanks, Dinesh 
1 answers

Passwords do not change themselves, so either the user is entering a different password then entered on the reset or the rest is retrieving the wrong user based on some identifier and users are resetting other user’s passwords.

I would check the flow resetting the passwords to exclude the last option