Azure production slot hangs up when first name of "ruby" is entered

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C#

Azure

I have a .NET Framework Web Forms C# application running in Azure. It contains an ASP Wizard that collects data for a marriage application. We recently had 2 instances of this same problem. When the users enter "Ruby" for any of the 4 parent first name fields, the Next button works on the entry steps, but once the review step is displayed, that lists all of the data entered so far (including "Ruby"), then the Next, Previous, and Cancel buttons do nothing. No error messages are displayed.

This does not occur when I run the application in Visual Studio, so I can't tell what is happening. It also does not occur in the Azure Staging slot.

This is such a bizarre problem, and it makes no sense!

What I have tried:

If I enter "Ruby" for any of the last name fields in Production, it works fine. If I enter "RubyRed" for any of the first name fields, it has the same problem, but if I enter "RedRuby" for any of the first name fields, it works fine.

Since it works in the Staging slot, I tried just swapping the Azure Production and Staging slots, but the Production slot still had the same issue after that.

I've done a lot of Googling and reading but haven't found anything that seems to help.