Item disappears in frame

I have clocks on the frames in my house, but they're no longer visible, even though they're still there. Even if I take them out and put them back, they remain invisible.

The strange thing is that this only happens with the clock, as I have other items on other frames and they're fine.

I don't know if it happens with other items, but for now, it's only happened with the clock.

P.S.: It happens on both the regular and the shiny frames.