Ah, it was originally the French, but I've googled and its been delayed to the Belgian GP as you've mentioned.Rule change coming for the Belgian GP to address the flexing issue. I don't know enough to know how much of a change it will make. @longers will probably have a better idea
My mate was suggesting that the block, at points, flexed way more than the 2mm that was allowed at the measure points. This was meant to produce drag.
He sad that the measurement will be across the block, which will mean that Red Bull (amongst others) may not get the grip they've been able to produce.
Supposedly, the manufactures have started to make adjustments so it's not one big chance when required.