It hasn't entered my head to group Blocks together, I can get images to disappear quite easily, and they don't always reappear by double-clicking the Scale Within Frame control. It may be coincidence, but I think if you add an image using the ALT drop, then remove it from the Block, there's a 50/50 chance one of the images will pop on the invisibility cloak. I'll have a go at grouping, so I can follow along.

I want to be fair though. The improvements are noticeable and welcome. I had problems with Stretch Full Width, random objects marking themselves invisible in the P&L Gallery, objects altering their layer position in a group. All these appear to work correctly now.

Talking of layers. I'm going to try adding layers to a page next.