Well, my suspicion is that you fat-fingered your password and that's what got saved.  If you go to the location I mentioned, there is a Manage Saved Passwords section.  I'd nuke the one for the website in question and go through the process of saving it again the next time you log in.
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Brian - Windows 10 Pro, 64-Bit, Version 20H2, Build 19042

Journalism 101:  If someone says it’s raining and another person says it’s dry, it’s not your job to quote them both. It’s your job to look out the f**king window and find out which is true.

      ~ Jonathan Foster (attributed)