This is a weird one and I'm hoping someone can tell me if PV has a glitch or it's just something stupid I did!
I've been rendering the same assembly now for several weeks as it progresses.
The first weirdness I noticed was the floor offset for reflections and shadows. Even though my assembly is located only 10" below the main top plane, I had to offset the floor a bit more than 200" to bring the floor up to the bottom of the model. It worked, so I've been rendering it that way since.
This evening I went to render another photo and my assembly disappeared, only the background rendered.
After about an hour of tweaking everything I could think of, I remembered the large offset, re-zeroed the floor and WAA-LAA my assembly is back and now only requires a 5" offset.
My assembly is still in the same place, 10" below the main top plane but now, well,... Any ideas what is going on?