custom weather popup only shows a blank popup

[Jklein03]

For a while the custom weather popup worked fine. Now when I open the weather popup, only a blank strip appears at the top of the screen (see screenschots).
I haven't change anything in my yaml. The popup just stopped working. Other custom popups still work and the issue is the same on all my devices/browsers.

Does anyone know what the issue could be?

Thanks!

Screenshots
default view:

when I try to open the popup:

- type: "custom:button-card"
        template: card_weather
        entity: weather.forecast_home_2
        variables:
          ulm_card_weather_name: " "
          ulm_card_weather_primary_info:
            - precipitation_probability
          ulm_card_weather_secondary_info:
            - wind_speed
          ulm_custom_popup:
            template: "popup_weather_forecast"
            entity: weather.forecast_home_2
            popup_variables:
              ulm_weather_popup_surpress_first_forecast: false