We can' tell - it needs your code running with your database, and we don't have access to either.
So, it's going to be up to you.
Fortunately, you have a tool available to you which will help you find out what is going on: the debugger. If you don't know how to use it then a quick Google for "Visual Studio debugger" should give you the info you need.
Put a breakpoint on the first line in the function, and run your code through the debugger. Then look at your code, and at your data and work out what should happen manually. Then single step each line checking that what you expected to happen is exactly what did. When it isn't, that's when you have a problem, and you can back-track (or run it again and look more closely) to find out why.
Sorry, but we can't do that for you - time for you to learn a new (and very, very useful) skill: debugging!
But ... encrypting passwords is a bad idea. There is some information on how to do it here: Password Storage: How to do it.
And remember: if this is web based and you have any European Union users then GDPR applies and that means you need to handle passwords as sensitive data and store them in a safe and secure manner. Text (even encrypted) is neither of those and the fines can be .... um ... outstanding. In December 2018 a German company received a relatively low fine of €20,000 for just that.