How to fix this frame contetn not working after a button press?

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C#

WPF

frame

I'm trying to put a page inside of a frame in code, it works fine when I call it from the main function. But when the button click event calls it, it does not change the frame's content. The frame within the page is already in a page in a frame if that has anything to do with it.

button click (gets called)

public void Water_icon_MouseDown(object sender, MouseButtonEventArgs e)
{
    Popup_handler(Popup_type.Water);
}

the switch works how it's supposed to

public void Popup_handler(Popup_type type)
{
    switch(type)
    {
        case Popup_type.Fertelizer:
            //Popup_frame.Content = new Popups.Fertilizer_popup(main_game);
            break;

        case Popup_type.Pest:
            //Popup_frame.Content = new Popups.Pest_popup(main_game);
            break;

        case Popup_type.Water:
            Popup_frame.Content = new Water_popup(main_game);
            break;

        case Popup_type.Air:
            //Popup_frame.Content = new Popups.Air_popup(main_game);
            break;

        case Popup_type.Light:
            //Popup_frame.Content = new Popups.Light_popup(main_game);
            break;
    }
}

Here's the frame, just in case:

<Frame x:Name="Popup_frame" Height="400" Grid.Row="1" 
       VerticalAlignment="Center" HorizontalAlignment="Right" 
       Width="1000" NavigationUIVisibility="Hidden"/>

What I have tried:

I checked the debugger and tested it separately, the page loads correctly and the inserted page works ok also. I tried the delegate because I thought it had to be something with threading, but it didn't work either. I have implemented something like this many times in this project already, but I never had this problem. Putting a different frame on the page doesn't work, changing the inserted page doesn't work either.