Almost certainly, it's been hidden by your error handling:
Never "swallow" exceptions:
Catch ex As Exception
Report them to the user, log them, do something
with them, or don't bother with Try ... Catch at all.
When you swallow an exception, you throw away all the information that helps you fix a problem - you even throw away the fact that there was a problem in the first place, so it shows up later as a more serious and harder to identify and fix problem.
And we can't tell what is happening here as a result - and even if we could, we couldn;t test it because we don't have any access to your data.
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!