Icons SVG not showing

I have a issue, i am sure that is something i do wrong.
i have an widget that i use with custom icons in config.
I see one icon when is ON the button, but when is off is not showing.

What i did wrong?
icons are different one is with on and one with off…
Thank you for your time:)

house-on.svg ( this works ) vs. house_off.svg ( this does not work ) thus it most probably has to be named house-off.svg ( dash instead of underscore ).