Updated to the latest build (4.8.6) of LXBeams. Opened a file from about a month ago. All pasted graphics in section view had disappeared. It also seemed impossible to paste a new graphic in or even draw a line in section view.
I had to get the work done quickly so I immediately reverted to version 4.8.5, and all the graphics appeared in section view. Surprisingly there was a whole lot of extra content. It seems as though everything I'd tried to do in version 4.8.6 had happened and saved into the file, it just wasn't visible on screen.
Sorry I can't give you any further information. I should be able to try and recreate the problem again in a couple of days if it would be helpful?
Macbook Pro Retina, MacOS 10.12.4