UPGRADE_WARNING: Event TextChanged may fire when form is initialized in VB

It's a warning, there isn't necessarily anything to fix. How best to fix it if it is a problem , is going to depend upon your usage -- you could check Page.IsPostBack, set your own boolean, check whatever fails when it's called and then make changes so that it doesn't fail, change how you register the event, lots of choices.

I would recommend that until you have an actual problem, just delete the comment. It's probably helped you as much as it can -- it has made you aware of a potential change in behavior, which you can keep in the back of your mind if you see a problem with the new behavior.