render frame keeps changing randomly

So I’m working on this model and I press f12 regularly to preview and out of nowhere it started rendering it as if there was no lights in the seen, just a black shape. I thought I might have hit some setting and I messed around a bit pressing ‘shadow’ and few other things and eventually it rendered properly but now its on and off, sometimes it renders in full sometimes its just a black shape without me doing anything… wats gives?

so now i have to press it twice, the first one is always just a dark shape and the second is a proper render