Explode Not Working

I have several sheets in my layout file each with a viewport. Some sheets have three viewports. The explode command is not working properly. I can successfully explode the viewport on sheet 1, but cannot explode the viewport on sheet 2. The command is there, but nothing happens when I click on it. The viewport is still there. On the sheet with three viewports, I can successfully explode one, but not the others.
Any hints on what might be happening.

UPDATE: Of the 18 sheets in my LO file, only three have the problem with the explode command. I discovered that when I tried to explode a viewport, the program created a folder with an image of the viewport rather than exploding the viewport.

If the viewport is rendered as raster or hybrid, a raster image will be created. If the viewport is rendered as Vector, you’ll get lines.

Thanks DaveR. That was it exactly. The viewports in question were rendered raster. So simple, just didn’t see it.
Thanks again.