WordPress password change isn't working

I don’t know why but my password is not working even though I keep ‘changing’ it to be the same thing. I haven’t had this problem with the dozens of other wordpress websites I’ve built. And I find it highly unlikely that someone else is being sneaky by hacking in and changing the passwords on me (for my account and one other user). Because nobody would have anything to gain from controlling this site while blocking others out

Anyone familiar with this issue? The client I built this site for is frustrated that they can’t log in even though I know I keep making sure the username and password are set exactly as they should be, case-sensitive and all